Postural changes in blood pressure and the prevalence of orthostatic hypotension among home-dwelling elderly aged 75 years or older.

This cross-sectional analysis of a population-based cohort investigates the postural changes in blood pressure (BP) and heart rate and assesses the prevalence of orthostatic hypotension (OH) and its associations with the medicines used by an elderly population. The study population (n=1000) was a random sample of persons aged 75 years or older in the City of Kuopio, Finland. In 2004, altogether, 781 persons participated in the study. After the exclusion of persons living in institutional care (n=82) and those without orthostatic test (n=46), the final study population comprised 653 home-dwelling elderly persons. OH was defined as a > or =20 mm Hg drop of systolic BP or a > or =10 mm Hg drop of diastolic BP or both 1 or 3 min after standing up from supine position. Systolic BP dropped for more than half of the home-dwelling elderly when they stood up from a supine to a standing position. The total prevalence of OH was 34% (n=220). No significant gender or age differences were seen. The prevalence of OH was related to the total number of medicines in regular use (P<0.05). OH and postural changes in BP are more common among the home-dwelling elderly than reported in previous studies. The prevalence of OH is related to the number of medicines in regular use. There is an obvious need to measure orthostatic BP of elderly persons, as low BP and OH are important risk factors especially among the frail elderly persons.

Evaluation of the current status of operating and closed landfills in Russia, Finland and Ireland with regard to water pollution and methane emission.

The annual production of municipal solid wastes (MSW) in Russia, Finland and Ireland in the late 1990s accounts for 37.5, 2.5 and 2.05 min. tonnes or 252, 488 and 566 kg per capita, respectively. 96.5, 64 and 91% of these wastes (for Russia, Finland and Ireland, correspondingly) are currently disposed of via landfilling. However, nowadays, MSW management in these countries is undergoing drastic changes (source separation, closure of old landfills, reduction of the number of landfills etc.) forced by recent legislation set by the European Union and Russian authorities. This paper evaluates the current status of MSW landfills, as well as information on current leachate and methane emissions in the three above mentioned countries. Landfill leachates are highly variable in each country and between different countries due to different rainfall and climatic conditions and also due to poor landfill top insulation/cover. Leachates in poorly structured landfills are very dilute, whereas leachates with total COD and nitrogen contents as high as 33,700 mg COD/l and 4,030 mg N/l, respectively, have been detected from state-of-the-art sites. Currently, on-site treatment of leachates exists at only a few landfills in Russia, Finland and Ireland but this situation will be considerably improved during the next years. The annual methane emissions from landfills are estimated as 500-900 and 77 ktonnes for Russia and Finland, respectively. Recent estimates from Ireland suggest an annual landfill methane emission of c. 2.1 Mt CO2 equivalent. Several systems of methane recovery have been developed in all three countries and these are currently in different stages of implementation.

Prediction of atrial fibrillation after coronary artery bypass grafting by measuring atrial peptide levels and preoperative atrial dimensions.

OBJECTIVE: We prospectively tested the hypothesis that atrial enlargement and increased level of atrial natriuretic peptide, N-terminal atrial natriuretic peptide and brain natriuretic peptide would predict atrial fibrillation after coronary artery bypass grafting. METHODS: Eighty-eight elective coronary artery bypass grafting patients had preoperative echocardiographic assessment. The level of atrial natriuretic peptide, N-terminal atrial natriuretic peptide and brain natriuretic peptide were measured preoperatively. Patients were ECG- monitored during the whole hospital stay. RESULTS: Thirty one (35.2%) patients had postoperative atrial fibrillation. In univariate analysis increased age (P=0.003), enlargement of left and right atria (P=0.002 and P=0.004, respectively) and increased level of preoperative atrial natriuretic peptide and N-terminal atrial natriuretic peptide (P=0.016 and P=0.03, respectively) were associated with postoperative atrial fibrillation. There was correlation between the age and level of N-terminal atrial natriuretic peptide (r=0.45 and P<0.001). In multivariate analysis only age and the left atrial enlargement were independent predictors of postoperative atrial fibrillation (P=0.02 and P=0.01). CONCLUSION: Left atrial enlargement was independent predictor for postoperative atrial fibrillation. However, atrial peptides were associated with age and did not independently predict postoperative atrial fibrillation. In addition, the wide variation of the peptide levels renders the implementation of this measure in clinical practice superfluous.

Biological nitrogen removal from municipal landfill leachate: low-cost nitrification in biofilters and laboratory scale in-situ denitrification.

The slow leaching of nitrogen from solid waste in landfills, resulting in high concentrations of ammonia in the landfill leachate, may last for several decades. The removal of nitrogen from leachate is desirable as nitrogen can trigger eutrophication in lakes and rivers. In the present study, a low-cost nitrification-denitrification process was developed to reduce nitrogen load especially in leachates from small landfills. Nitrification was studied in laboratory and on-site pilot aerobic biofilters with waste materials as filter media (crushed brick in upflow filters and bulking agent of compost in a downflow filter) while denitrification was studied in a laboratory anoxic/anaerobic column filled with landfill waste. In the laboratory nitrification filters, start-up of nitrification took less than 3 weeks and over 90% nitrification of leachate (NH4-N between 60 and 170mg N l(-1), COD between 230 and 1,300 mg l(-1)) was obtained with loading rates between 100 and 130 mgNH4-N l(-1) d at 25 degrees C. In an on-site pilot study a level of nitrification of leachate (NH4-N between 160 and 270 mg N l(-1), COD between 1,300 and 1,600 mg l(-1)) above 90% was achieved in a crushed brick biofilter with a loading rate of 50mg NH4-N l(-1) d even at temperatures as low as 5-10 degrees C. Ammonium concentrations in all biofilter effluents were usually below the detection limit. In the denitrification column. denitrification started within 2 weeks and total oxidised nitrogen in nitrified leachate (TON between 50 and 150mg N l(-1)) usually declined below the detection limit at 25 degrees C, whereas some ammonium, probably originating from the landfill waste used in the column, was detected in the effluent. No adverse effect was observed on the methanation of waste in the denitrification column with a loading rate of 3.8 g TON-N/t-TS(waste) d. In conclusion, nitrification in a low-cost biofilter followed by denitrification in a landfill body appears applicable for the removal of nitrogen in landfill leachate in colder climates.

Screening of physical-chemical methods for removal of organic material, nitrogen and toxicity from low strength landfill leachates.

Physical-chemical methods have been suggested for the treatment of low strength municipal landfill leachates. Therefore, applicability of nanofiltration and air stripping were screened in laboratory-scale for the removal of organic matter, ammonia, and toxicity from low strength leachates (NH4-N 74-220 mg/l, chemical oxygen demand (COD) 190-920 mg O2/l, EC50 = 2-17% for Raphidocelis subcapitata). Ozonation was studied as well, but with the emphasis on enhancing biodegradability of leachates. Nanofiltration (25 degrees C) removed 52-66% of COD and 27-50% of ammonia, the latter indicating that ammonia may in part have been present as ammonium salt complexes. Biological pretreatment enhanced the overall COD removal. Air stripping (24 h at pH 11) resulted in 89% and 64% ammonia removal at 20 and 6 degrees C, respectively, the stripping rate remaining below 10 mg N/l h. COD removals of 4-21% were obtained in stripping. Ozonation (20 degrees C) increased the concentration of rapidly biodegradable COD (RBCOD), but the proportion of RBCOD of total COD was still below 20% indicating poor biological treatability. The effect of the different treatments on leachate toxicity was assessed with the Daphnia acute toxicity test (Daphnia magna) and algal growth inhibition test (Raphidcocelis subcapitata). None of the methods was effective in toxicity removal. By way of comparison, treatment in a full-scale biological plant decreased leachate toxicity to half of the initial value. Although leachate toxicity significantly correlated with COD and ammonia in untreated and treated leachate, in some stripping and ozonation experiments toxicity was increased in spite of COD and ammonia removals.

Evaluation of kinetic coefficients using integrated monod and haldane models for low-temperature acetoclastic methanogenesis.

The integrated Monod and Haldane models were used to evaluate the kinetic coefficients and their standard deviations using the methane accumulation curves of low-temperature acetoclastic methanogenesis. The linear and exponential approximations and the limitations of their applicability were deduced from the integrated models. The samples of lake sediments and biomass taken from a low-temperature upflow anaerobic sludge blanket (UASB) reactor were used as inoculum in batch assays for acetate methanation. In comparison, the Monod and Haldane models were applied to evaluate the kinetic coefficients for mesophilic acetoclastic methanogenesis accomplished by the pure culture of Methanosarcina barkeri strain MS. The Monod and Haldane models and their approximations were fitted by using non-linear regression. For the wide range of initial acetateconcentrations (4.2-84 mM: 5-100 mM) applied to the UASB biomass at 11 and 22 degrees C and for the lake sediment samples at 6 and 15 degrees C, a better fit was obtained with the Haldane models and their exponential approximations, respectively. For the lake sediments the values of inhibition coefficients decreased at decreasing temperatures. At the highest temperature of 30 degrees C no difference was found between the Haldane and Monod models and the simpler Monod model should be preferred. The values of the maximum growth rate of biomass were highest at 30 degrees C (lake sediment) and 22 degrees C (the UASB biomass) being in a range presented in the literature for mesophilic acetoclastic methanogenesis.

Adverse ocular effects of flecainide.

PURPOSE: To study if flecainide has ocular adverse effects. METHODS: Both eyes of 38 flecainide medicated patients were thoroughly examined including colour vision, contrast sensitivity and visual fields. RESULTS: 10.5% of the patients had blurred vision on lateral gaze lasting for a couple of seconds. Small corneal deposits were found in 14.5% of the patients. All visual function tests were normal. CONCLUSION: Flecainide seems to be a safe drug with minimal ocular adverse effects.

Ozone-sensitive arabidopsis rcd1 mutant reveals opposite roles for ethylene and jasmonate signaling pathways in regulating superoxide-dependent cell death.

We have isolated a codominant Arabidopsis mutant, radical-induced cell death1 (rcd1), in which ozone (O(3)) and extracellular superoxide (O(2)(*)-), but not hydrogen peroxide, induce cellular O(2)(*)- accumulation and transient spreading lesions. The cellular O(2)(*)- accumulation is ethylene dependent, occurs ahead of the expanding lesions before visible symptoms appear, and is required for lesion propagation. Exogenous ethylene increased O(2)(*)--dependent cell death, whereas impairment of ethylene perception by norbornadiene in rcd1 or ethylene insensitivity in the ethylene-insensitive mutant ein2 and in the rcd1 ein2 double mutant blocked O(2)(*)- accumulation and lesion propagation. Exogenous methyl jasmonate inhibited propagation of cell death in rcd1. Accordingly, the O(3)-exposed jasmonate-insensitive mutant jar1 displayed spreading cell death and a prolonged O(2)(*)- accumulation pattern. These results suggest that ethylene acts as a promoting factor during the propagation phase of developing oxyradical-dependent lesions, whereas jasmonates have a role in lesion containment. Interaction and balance between these pathways may serve to fine-tune propagation and containment processes, resulting in alternate lesion size and formation kinetics.

Cardiac adrenergic innervation within the first 3 months after acute myocardial infarction.

It is widely accepted that myocardial infarction results in adrenergic denervation of the infarcted and peri-infarcted myocardium. On the contrary, the concept of re-innervation of adrenergic nerve fibres is less well established. Although there is evidence of partial re-innervation occuring several months after myocardial infarction, the extent and time scale of re-innervation are only poorly known. In this study we investigated changes in cardiac adrenergic innervation and myocardial perfusion during the early convalescence period (the first 3 months) after an acute myocardial infarction. Single-photon emission computed tomographic imaging was conducted in 15 men 1 week and 3 months after an acute myocardial infarction with I123-metaiodobentzylguanidine (MIBG) and Tc99m-sestamibi (MIBI) to determine the extent of adrenergic denervation and impaired perfusion, respectively. A MIBG and MIBI defect was determined as regional uptake

Cardiac adrenergic denervation in patients with non-Q-wave versus Q-wave myocardial infarction.

In spite of smaller infarct size and better preserved left ventricular function the long-term prognosis after a non-Q-wave infarction is not better than after a Q-wave infarction. In fact, the risk of sudden cardiac death is higher in patients with a non-Q-wave infarction than in patients with a Q-wave infarction. One possible reason for postinfarction arrhythmias is cardiac adrenergic denervation resulting from myocardial infarction. In this study we compared cardiac adrenergic innervation after non-Q-wave and Q-wave infarctions. Single-photon emission tomography using iodine-123 metaiodobentzylguanidine (MIBG) and technetium-99m sestamibi (MIBI) tracers were conducted in order to compare cardiac adrenergic denervation and myocardial perfusion in 12 patients with a non-Q-wave infarction and 15 patients with a Q-wave infarction. MIBG and MIBI defects were determined as regional uptake < or = 30% of maximal myocardial activity. The size of MIBI defects calculated as a percentage of left ventricular mass was significantly smaller in patients with a non-Q-wave infarction than in patients with a Q-wave infarction (4%+/-3% vs 9%+/-7%, P<0.05, respectively). According to the maximal serum creatine kinase activity, less myocardium was damaged in patients with a non-Q-wave infarction than in patients with a Q-wave infarction (502+/-436 IU/l vs 1878+/-1265 IU/l, P<0.001). In spite of this, the extent of MIBG defects was similar in patients with a non-Q-wave and patients with a Q-wave infarction (21%+/-18% vs 23%+/-12%, respectively). In addition, the size of MIBG defect correlated with the infarct size (maximal creatine kinase activity) (r=0.52, P<0.05) after a Q-wave infarction but not after a non-Q-wave infarction. In conclusion, despite a smaller infarct size in non-Q-wave infarct patients, the extent of cardiac adrenergic denervation was similar in patients with a non-Q-wave and patients with a Q-wave infarction. In addition, the extent of cardiac adrenergic denervation was related to the infarct size in patients with a Q-wave infarction but not in patients with a non-Q-wave infarction.

Similar effect of revascularization on technetium-99m( )sestamibi and 15-(p-iodophenyl)pentadecanoic acid uptake in myocardial infarction patients.

To study its usefulness as a tracer for assessment of the perfusion and viability of myocardium, 15-(p-iodophenyl)pentadecanoic acid (IPPA) was compared with technetium-99m sestamibi (MIBI). Dual-tracer single-photon emission tomography rest imaging was performed no more than 2 months before and 3 months after coronary artery bypass grafting in 28 patients with previous anterior (n=13) or inferior (n=15) infarction. The size of MIBI and IPPA defects decreased from 14%+/-12% and 13%+/-9% to 10%+/-11% and 9%+/-7%, respectively (P<0.001 for both). The MIBI uptake increased in the infarct zones from 35%+/-11% to 43%+/-8% (P<0.001), and in the peri-infarct zones from 50%+/-11% to 55%+/-10% (P<0.05). The IPPA uptake increased in the infarct zones from 37%+/-11% to 44%+/-13% (P<0.001), and in the peri-infarct zones from 51%+/-11% to 57%+/-12% (P<0.05). In nine patients with improved regional echocardiographic wall motion score after bypass surgery, the pre-operative uptake values of both MIBI and IPPA in the infarct and peri-infarct zones were on average slightly but not significantly higher than in 19 patients with no observed improvement in regional wall motion score. In patients with improved regional wall motion, the MIBI scans and the IPPA scans showed (non-significant) decreases in defect size and increases in infarct and peri-infarct zone uptake after bypass surgery. Similar (in some cases significant) changes were observed in the patients without improvement in wall motion. Thus IPPA and MIBI provided similar information about perfusion and viability in pre- and postoperative evaluation of patients with clinically evident myocardial infarction and with normal global ejection fraction. Regardless of the tracer used, the resolution capability of the dual-tracer method with a rest imaging protocol was not sufficient to differentiate viable from non-viable infarction defects in unselected individual patients with a normal ejection fraction.

Virus-specific capping of tobacco mosaic virus RNA: methylation of GTP prior to formation of covalent complex p126-m7GMP.

In capping cellular mRNAs, a covalent GMP-enzyme intermediate leads to formation of G(5')ppp(5')N at the 5' end of the RNA, which is modified by methylation catalyzed by guanine-7-methyltransferase. Here we show that isolated membranes from tobacco mosaic virus (TMV)-infected plant or insect cells expressing TMV replicase protein p126, synthesized m7GTP using S-adenosylmethionine (AdoMet) as the methyl donor, and catalyzed the formation of a covalent guanylate-p126 complex in the presence of AdoMet. The methyl group from AdoMet was incorporated into p126, suggesting that the complex consisted of m7GMP-p126. Thus, TMV and alphaviruses, despite their evolutionary distance, share the same virus-specific capping mechanism.

Transit time heterogeneity of bolus flow through the heart and lungs in patients with left-to-right intracardiac shunt.

Knowledge of the contributions of transit time heterogeneity to the cardiopulmonary system is important for understanding cardiopulmonary function in patients with intracardiac shunt. We determined the heterogeneity of blood transit times occurring between the right atrium and the left ventricle. Eighty two patients with suspected left-to right shunt were investigated with first-pass 99mTc-labelled red blood cell radiocardiography at supine rest. Forty two of them had a pulmonary-to-systemic flow ratio (Qp:Qs) of less than 1.2 and they served as a control group. The remaining study subjects had a Qp:Qs ratio of 1.7 +/- 0.3 (mean +/- SD). The patients with shunt had significantly greater (p < 0.001) heterogeneity of transit times (49 +/- 9%) than in the controls (39 +/- 7%). Overall heterogeneity of cardiopulmonary transit times in patients with shunt showed a curvature relationship; the highest values were centred in patients with moderate to severe shunt (1.5 < Qp:Qs < 2.5). The results suggest that the increased heterogeneity of transit times mainly occurs within the pulmonary capillary bed in patients with intracardiac shunt. This is probably due to the recruitment of the open capillaries without vessel distension.

Complications related to permanent pacemaker therapy.

This study evaluates complications related to permanent endocardial pacing in the era of modern pacemaker therapy. There is only limited information available about the complications related to modern cardiac pacing. Most of the existing data are based on the 1970s and are no longer valid for current practice. The recent reports on pacemaker complications are focused on some specific complication or are restricted to early complications. Thus, there are no reports available providing a comprehensive view of complications related to modern cardiac pacing. Four hundred forty-six patients, who received permanent endocardial pacemakers between January 1990 and December 1995 at Kuopio University Hospital, were reviewed retrospectively using patient records. Attention was paid to the occurrence of any complication during the implantation or follow-up. An early complication was detected in 6.7%, and 4.9% of patients were treated invasively due to the early complication. Late complication developed in 7.2% and reoperation was required in 6.3% of the patients. Complications related to the implantation procedure occurred in 3.1%. Inadequate capture or sensing was observed in 7.4% of the patients. Pacemaker infection was detected in 1.8% and erosion in 0.9% of the patients. An AV block developed in 3.6% (1.6%/year) patients who received an AAI(R)-pacemaker due to sick sinus syndrome. There was no mortality attributable to pacemaker therapy. A great majority (68%) of the complications occurred within the first 3 months after the implantation. Complications associated to modern permanent endocardial pacemaker therapy are not infrequent. Eleven percent of patients needed an invasive procedure due to an early or late complication.

Prevalence and natural course of ectopic atrial tachycardia.

AIMS: The purpose of this study was to calculate the prevalence of ectopic atrial tachycardia in a population of young asymptomatic males and to assess its natural course both in asymptomatic subjects and in symptomatic hospital patients. METHODS AND RESULTS: 12-lead electrocardiograms (ECG) of 3554 consecutive males applying for a pilot's licence were analysed. ECGs of symptomatic arrhythmia patients at two university hospitals were also analysed. A repeat ECG was taken in cases of ectopic atrial tachycardia to assess the natural course of this arrhythmia. Twelve out of 3554 asymptomatic subjects (prevalence 0.34%) and 17 out of 3700 symptomatic arrhythmia patients (prevalence 0.46%) had ECG evidence of ectopic atrial tachycardia. A repeat ECG was obtained after a mean follow-up of 8+/-3 years in asymptomatic subjects and 7+/-3 years in symptomatic patients. After the follow-up, seven (26%) out of 27 patients were still in a similar ectopic atrial rhythm, 10 (37%) showed a change in P wave morphology and 10 (37%) were in sinus rhythm. Heart rate was significantly slower (mean rate 81+/-19 vs 109+/-17 beats. min-1) in the repeat ECGs. CONCLUSION: Asymptomatic ectopic atrial tachycardia is not an uncommon finding in a population of young males. The majority of patients show slowing of heart rate in the course of time, either with restoration of sinus rhythm or with a change in P wave morphology, suggesting that the ectopic foci undergo gradual degeneration with time.

Cardiac sympathetic denervation in patients with coronary artery disease without previous myocardial infarction.

Myocardial infarction damages sympathetic nerve fibers coursing through the infarct zone. In this study we investigated whether coronary artery disease without myocardial infarction results in sympathetic denervation. We examined 12 patients without a history of previous myocardial infarction and 19 postinfarction patients. 1-123 metaiodobenzylguanidine (MIBG) and technetium-99m sestamibi (MIBI) single-photon emission tomography were conducted at rest to determine the extent of denervated myocardium and the extent of myocardium with reduced perfusion, respectively. In addition, myocardial perfusion during exercise was assessed with MIBI. A MIBG or MIBI defect was determined as being regional uptake of < or =30% of the maximal myocardial activity. All but 1 patient without previous infarction had MIBG defects. MIBG defects (10.3 +/- 8.5% of left ventricular mass) were significantly larger than MIBI defects at rest (2.4 +/- 3.2%, p <0.001) and during exercise (4.8 +/- 6.1%, p <0.05). In multiregression analysis, the size of an MIBG defect was associated with severity of coronary stenoses (> or =90% of lumen diameter; p <0.05), but not with age, number of significant stenoses (> or =50% of lumen diameter), left main disease, functional class, left ventricular ejection fraction, angina pectoris, maximal ST depression, or mean workload during exercise test. MIBG and MIBI defects were significantly larger in patients with severe coronary stenoses than in patients with moderate stenoses (50% to 89% of lumen diameter) (16.4 +/- 8.9% vs 6.0 +/- 5.2% [p <0.05] and 5.0 +/- 3.1% vs 0.6 +/- 1.3% [p <0.001], respectively). The size of MIBG (16.1 +/- 8.9%) and MIBI defects (7.3 +/- 6.5%) at rest in postinfarction patients did not differ from patients with severe stenoses. Our study demonstrates that cardiac adrenergic tissue is very sensitive to ischemia and that regional cardiac sympathetic denervation can occur in patients with stable coronary artery disease without previous myocardial infarction.

Transcriptional and translational adjustments of psbA gene expression in mature chloroplasts during photoinhibition and subsequent repair of photosystem II.

The D1 reaction centre protein of photosystem II (PSII), encoded by the plastid psbA gene, has the highest turnover rate of all thylakoid proteins, due to light-induced damage to D1. The expression of the psbA gene was studied in chloroplasts of fully developed pea (Pisum sativum L.) leaves during high-light photoinhibitory treatment and subsequent restoration of PSII function at low light. psbA transcript levels were determined and the translational activity was followed by in vivo pulse-labelling, by in vitro translations with intact chloroplasts, and by run-off translations on isolated thylakoid membranes. PSII photochemical efficiency was determined in vivo by monitoring the ratio of variable fluorescence to maximal fluorescence (F(V)/F(M)). Enhanced D1 synthesis in pea leaves, upon a shift first from darkness to growth light and subsequently to high light, was accompanied by a substantial increase in the total number of pshA transcripts and by the accumulation of psbA mRNA x initiation complexes on thylakoid membrane. This suggested that high-light illumination increased the transcriptional activity of the psbA gene in mature leaves, and that enhanced translational initiation of psbA mRNA was followed by docking of the initiation complexes to the thylakoid membrane. The high-light-induced increase in the number of thylakoid-associated psbA mRNA x initiation complexes, occurred in parallel with enhanced in vivo D1 synthesis. This, however, did not result in an enhanced accumulation of D1 translation products in in vitro run-off translations when pea leaves were shifted from growth light to high light. This may suggest that at high light only a portion of thylakoid-associated psbA mRNA can be under translational elongation at a given moment. When the leaves were shifted from high light to low light to allow repair of PSII, thylakoid-associated psbA mRNA was rapidly released from the membrane and the high-light-induced pool of psbA transcripts was degraded. The synthesis of the D1 protein decreased on the same time scale. However, the restoration of PSII photochemical function, measured as F(V)/F(M), took a substantially longer time. It is concluded that during changing light conditions, mature leaves are able to adjust psbA gene expression both at the transcriptional and at the translational level.

Synthesis and assembly of the D1 protein into photosystem II: processing of the C-terminus and identification of the initial assembly partners and complexes during photosystem II repair.

In previous studies [van Wijk, K. J., Bingsmark, S., Aro, E.-M., & Andersson, B. (1995) J. Biol. Chem. 270, 25685-25695; van Wijk, K. J., Andersson, B., & Aro, E.-M. (1996) J. Biol. Chem 271, 9627-9636], we have demonstrated that D1 protein synthesized in isolated chloroplasts and thylakoids is incorporated into the photosystem II (PSII) core complex. By pulse-chase experiments in these in vitro systems, followed by sucrose gradient fractionation of solubilized thylakoid membranes, it was shown that this assembly proceeded stepwise; first the D1 protein was incorporated to form a PSII reaction center complex (PSII rc), and through additional assembly steps the PSII core complex was formed. In this study, we have analyzed this assembly process in more detail, with special emphasis on the initial events, through further purification and analysis of the assembly intermediates by nondenaturing Deriphat-PAGE and by flatbed isoelectric focusing. The D2 protein was found to be the dominant PSII reaction center protein initially associating with the new D1 protein. This strongly suggests that the D2 protein is the primary "receptor" or stabilizing component during or directly after synthesis of the D1 protein. After formation of the D1-D2 heterodimer, cyt b559 became attached, whereas the psbI gene product was assembled as a subsequent step, thereby forming a PSII reaction center complex. Subsequent formation of the PSII core occurred by binding of CP47 and then CP43 to the PSII rc. The rapid radiolabeling of a minor population of a PSII core subcomplex without CP43 indicated that an association of newly synthesized D1 protein with a preexisting complex consisting of D2/cyt b55q/psbI gene product/CP47 was possibly occurring, in parallel to the predominant sequential assembly pathway. The kinetics of synthesis and processing of the precursor D1 protein were followed in isolated chloroplasts and were compared with its incorporation into PSII assembly intermediates. No precursor D1 protein was found in PSII core complexes, indicating either that incorporation into the PSII core complex facilitates the cleavage of the C-terminus or, more likely, that processing is more rapid than the assembly into the PSII core.