Molecular cloning and expression analyses of mitochondrial and plastidic isoforms of cysteine synthase (O-acetylserine(thiol)lyase) from Arabidopsis thaliana.

Cysteine synthase, the key enzyme for fixation of inorganic sulfide, catalyses the formation of cysteine from O-acetylserine and inorganic sulfide. Here we report the cloning of cDNAs encoding cysteine synthase isoforms from Arabidopsis thaliana. The isolated cDNA clones encode for a mitochondrial and a plastidic isoform of cysteine synthase (O-acetylserine (thiol)-lyase, EC 4.2.99.8), designated cysteine synthase C (AtCS-C, CSase C) and B (AtCS-B; CSase B), respectively. AtCS-C and AtCS-B, having lengths of 1569-bp and 1421-bp, respectively, encode polypeptides of 430 amino acids (approximately 45.8 kD) and of 392 amino acids (approximately 41.8 kD), respectively. The deduced amino acid sequences of the mitochondrial and plastidic isoforms exhibit high homology even with respect to the presequences. The predicted presequence of AtCS-C has a N-terminal extension of 33 amino acids when compared to the plastidic isoform. Northern blot analysis showed that AtCS-C is higher expressed in roots than in leaves whereas the expression of AtCS-B is stronger in leaves. Furthermore, gene expression of both genes was enhanced by sulfur limitation which in turn led to an increase in enzyme activity in crude extracts of plants. Expression of the AtCS-B gene is regulated by light. The mitochondrial, plastidic and cytosolic (Hesse and Altmann, 1995) isoforms of cysteine synthase of Arabidopsis are able to complement a cysteine synthase-deficient mutant of Escherichia coli unable to grow on minimal medium without cysteine, indicating synthesis of functional plant proteins in the bacterium. Two lines of evidence proved that AtCS-C encodes a mitochondrial form of cysteine synthase; first, import of in vitro translation products derived from AtCS-C in isolated intact mitochondria and second, Western blot analysis of mitochondria isolated from transgenic tobacco plants expressing AtCS-C cDNA/c-myc DNA fusion protein.

Atrial pacing leads following open heart surgery: active or passive fixation?

The right atrial appendage is often amputated at the time of cardiopulmonary bypass. Because of concerns regarding lead displacement, use of active fixation atrial leads has been recommended in patients who require permanent atrial or dual chamber pacing after open heart surgery. We evaluated the acute and chronic performance of active and passive fixation atrial leads implanted at our institution between 1985 and 1993 in patients with previous open heart surgery. Of 78 consecutive patients, 38 had an active fixation atrial lead, 28 had a passive fixation steroid-eluting lead, and 12 had a passive fixation lead without steroid-eluting properties. At implantation, sensed P wave amplitudes were similar in the three groups, but lead impedance and threshold were significantly higher for active fixation leads compared to all passive fixation leads. During follow-up, atrial pacing thresholds were significantly higher, and sensed P wave amplitudes significantly lower, in the patients with active fixation leads compared to those with passive fixation leads. Loss of sensing occurred in 6 of 38 (16%) patients with active fixation leads and 1 of 40 (2.5%) patients with a passive fixation lead (P = 0.027). Atrial lead displacement occurred in two patients with active fixation leads and one with a passive fixation lead. Comparison with a parallel group of patients without previous open heart surgery demonstrated that atrial lead performance was similar in the two groups. We conclude that, when permanent atrial or dual chamber pacing is necessary in patients with prior open heart surgery, it is appropriate to implant a passive fixation atrial lead except on the infrequent occasions when a stable atrial position cannot be obtained.

Schedule- and dose-intensified paclitaxel as weekly 1-hour infusion in pretreated solid tumors: results of a phase I/II trial.

Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) has been studied primarily on a 3-week schedule as a 3-, 24-, or 96-hour infusion at doses ranging from 135 to 250 mg/m2. The observed toxicity profile seems to be both dose and schedule dependent. Dose densification of paclitaxel given weekly over 6 weeks on a split-dose schedule for an overall increase in dose intensity was thought to improve the therapeutic index of paclitaxel in a variety of advanced malignancies and to be suitable for outpatient administration. For this study, chemotherapy consisted of a weekly 1-hour infusion of paclitaxel at a starting dose of 40 mg/m2/wk for 6 weeks, followed by a 2- to 3-week interval. Paclitaxel dosage was escalated in 10 mg/m2/wk increments in subsequent patients, to a maximum dosage of 90 mg/m2/wk. Intravenous dexamethasone, cimetidine, clemastine, and ondansetron were administered immediately before the paclitaxel infusion. Fifty patients participated in the study. The male to female ratio was 21 to 29, the median age was 53.2 years (age range, 33 to 74), and the median performance status was 1. All patients were chemotherapeutically pretreated. Overall response included five complete responses (10%), 15 partial responses (30%), 19 no change (38%), and 11 disease progressions (22%). Median dose intensity was 410 mg/m2/6 wk (range, 200 to 540 mg/m2/6 wk). Hematologic toxicity was mild, with no grade 3 or 4 toxicity up to 90 mg/m2/wk. No hypersensitivity reactions or neurologic or cardiac toxicities were documented. Dose-densified, weekly paclitaxel is concluded to be active in a variety of pretreated tumor entities. The overall low hematologic and peripheral toxicity profile suggests that further dose intensification of weekly paclitaxel and/or combination with other cytotoxic agents (eg, cisplatin/carboplatin, ifosfamide, etoposide) may be warranted. Paclitaxel can be given safely in the outpatient setting. Paclitaxel 90 mg/m2/wk is recommended for single-agent treatment. Dose-densified paclitaxel may be considered a valuable and promising alternative to standard 3-week treatment, with further options possible in combination chemotherapy.

The role of incompetence of the anterior cruciate and lateral ligaments in anterolateral and anteromedial instability. A biomechanical study of cadaver knees.

UNLABELLED: The anterolateral and anteromedial stability of seventeen fresh frozen cadaver knees was studied in a test apparatus designed to simulate physiological conditions. Statistically significant increases in internal rotation occurred in seven knees when only the anterior cruciate ligament was sectioned, and these increases were enhanced by subsequent sectioning of the posterolateral complex and the lateral collateral ligament, singly or in combination. On the other hand, sectioning of the posterolateral complex and of the lateral collateral ligament, leaving the anterior cruciate intact, did not produce significant increases in internal rotation until the anterior cruciate ligament was sectioned in seven knees. When the entire anterolateral capsule was sectioned as far posterior as the lateral collateral ligament in three knees, no changes in internal or external rotation occurred. Only when the posterolateral complex was sectioned was there a significant increase in external rotation in any of the ligament-sectioning sequences. Thus, it appears that for pathological internal rotation of the tibia on the femur to occur, the anterior cruciate ligament must be incompetent. CLINICAL RELEVANCE: The test apparatus and the results are useful in assessing which ligament structures contribute to clinically noted rotational knee instabilities.

Whiplash syndrome.

Whiplash, or cervical acceleration extension injury, is due predominantly to hyperextension and prolongation of the neck, with rebound flexion. A variety of disabling soft tissue injureries may result, including vertebral arter damage. While x-rays are generally unremarkable, they should be obtained. Rational management is based on rest, heat and analgesics, muscle relaxants, isometric exercises and an informed patient. The assumption that whiplash syndrome occurs only in neurotic or litigation-minded patients should be discouraged.

The effect of patellectomy on knee function.

Thirty-three patients were evaluated after patellectomy for subjective complaints, objective physical findings, quadriceps strength, and knee motion during activities of daily living. Partial and complete patellectomy caused an equal loss of active and passive range of motion. Complete patellectomy resulted in greater ligament instability, quadriceps atrophy, and loss of quadriceps strength compared with partial patellectomy. Complete patellectomy casued a reduction in the degree of stance-phase flexion during level walking and negotiating stairs.