Risk assessment of heavy metal toxicity by sensitive biomarker δ-aminolevulinic acid dehydratase (ALA-D) for onion plants cultivated in polluted areas in Kosovo.

Biomarkers allow an integrated risk assessment of heavy metal pollution effects in living organisms. In this study, the biochemical effects of Cd, Cr, Ni, Pb and Zn pollution in agricultural soil and their accumulation in Alium cepa L. (onion) were evaluated with ALA-D enzyme response as a biomarker, along with δ-aminolevulinic acid (ALA) and total chlorophyll contents in leaves of this plant. Soil samples were randomly selected from agricultural areas in two regions, Mitrovica and Obiliqi, which are considered the most industrially polluted regions in Kosovo. Results show that Pb and Zn concentrations in soil samples from Mitrovica (1953-2576 mg kg -1) and Obiliqi regions (138-179 mg kg -1) and their bioaccumulation levels in onion were significantly higher in comparison with the control group. There was an adverse negative correlation between Pb or Zn concentration and ALA-D activity and total chlorophyll content, and a positive correlation with ALA content. This study indicates that ALA-D activity can be used as a very sensitive biomarker for evaluation of heavy metal pollution. The bioaccumulation of heavy metals from soil polluted areas poses a threat for food contamination and public health.

Oral administration of diphenyl diselenide potentiates hepatotoxicity induced by carbon tetrachloride in rats.

Carbon tetrachloride (CCl4) is a model for studying free radical-induced liver injury and screening hepato-protective drugs. Numerous studies have reported the involvement of oxidative stress in CCl4-induced liver damage and the hepato-protective effects mediated by different antioxidants. The present study examined the effects of diphenyl diselenide, (PhSe)2, on hepatotoxicity induced by CCl4 in rats. To this end, male Wistar rats received (PhSe)2 by oral route at the dosage of 31.2 mg/kg for one or two days. After the second day of treatment, rats received CCl4 orally in a single dose. The liver and kidney were utilized for determination of histopathology, biochemical [aspartate (ALT) and alanine (AST) aminotransferases, alkaline phosphatase (ALP), total bilirrubin (TB) and gamaglutamyl transferase (GGT)] and toxicological parameters [thiobarbituric reactive species (TBARS) levels, catalase activity, ascorbic acid, nonprotein thiols (NPSH) and aminolevulinate dehydratase (-ALA-D) activity]. Repeated administration of (PhSe)2 caused a marked potentiation of hepatotoxicity induced by CCl4 exposure, as manifested by an increase in biochemical parameters (AST, ALT, ALP, GGT and BT) and severe alteration in histopathology. This study also demonstrated a potentiation of TBARS levels and a consequent depletion of important antioxidant defenses including catalase and ascorbic acid. Pre-treatment with a single dose of (PhSe)2 prevented the effect of strychnine, a substrate for CYPs, abolishing lethality in mice. This result indicates that (PhSe)2 prevented animal death, suggesting an activator action of (PhSe)2 in CYPs. This study clearly indicates that (PhSe)2 potentiated acute hepatic damage induced by CCl4.

Efficacy of 2,3-dimercapto-1-propanesulfonic acid (DMPS) and diphenyl diselenide on cadmium induced testicular damage in mice.

The deleterious effect of acute cadmium-intoxication in mice testes was evaluated. Animals received a single dose of CdCl2 (2.5 or 5 mg/kg, intraperitoneally) and a number of toxicological parameters in mice testes were examined, such as delta-aminolevulinic acid dehydratase (delta-ALA-D) activity, lipid peroxidation, hemoglobin and ascorbic acid contents. Furthermore, the parameters that indicate tissue damage such as plasma alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were also determined. Thus, a possible protective effect of 2,3-dimercapto-1-propane-sulfonic acid (DMPS) and diphenyl diselenide (PhSe)2 were studied. The results demonstrated an inhibition of delta-ALA-D activity, a reduction of ascorbic acid and an increase of lipid peroxidation induced by cadmium, indicating testes damage. Furthermore, we observed an increase of plasma LDH, AST and ALT activities. DMPS (400 mol/kg) and (PhSe)2 (100 micromol/kg) partially protected from the inhibitory effect of 2.5 mg/kg CdCl2 on delta-ALA-D and from the increase of TBARS (thiobarbituric acid reactive species) levels. (PhSe)2 therapy was effective in ameliorate ascorbic acid content when the cadmium dose was 2.5 mg/kg. Treatment with DMPS and (PhSe)2, individually or combined, was inefficient in reducing cadmium-induced plasma LDH and ALT activity increase. The use of combined therapy (DMPS plus (PhSe)2) proved to be efficient in decreasing cadmium levels in testes and in ameliorating plasma AST activity from animals that received the highest dose of cadmium.

Sensitivity of delta-ALA-D (E.C. 4.2.1.24) of rats to metals in vitro depends on the stage of postnatal growth and tissue.

Heavy metals, like cadmium, lead, and mercury, are potential toxic substances. The exposure to these metals can cause renal disturbances and neurological alterations. Young rats are more sensitive to harmful agents than adult animals. Delta-ALA-D enzyme acts as a biomarker of these exposures, since it has high affinity for divalent metals. The purpose of this search was to investigate the sensitivity of delta-ALA-D from suckling rats to cadmium, lead or mercury in vitro. IC(50) for delta-ALA-D activity of brain, kidneys, and liver from rats with ages between 1 and 6, 8 and 13 or 17 and 21 days was determined using metals concentrations that range from 0 to 200 microM for CdCl(2), 0 to 600 microM for HgCl(2) and from 0 to 50 microM for lead acetate. The results demonstrated that the cerebral delta-ALA-D activity is more sensitive to lead acetate than to cadmium and mercury. Delta-ALA-D from hepatic tissue is the most resistant to presence of mercury chloride in assay medium. Lead and cadmium are more toxic to renal enzyme than mercury. To sum up, the sensitivity of delta-ALA-D enzyme of young rats to heavy metals studied depends on the phase of development and tissue.

Cadmium induced testicular damage and its response to administration of succimer and diphenyl diselenide in mice.

Acute effects of cadmium in mice testes were evaluated. Animals received a single dose of CdCl2 (2.5 mg/kg or 5 mg/kg, intraperitoneally) and a number of toxicological parameters in mice testes were examined such as delta-aminolevulinic acid dehydratase (delta-ALA-D) activity, lipid peroxidation, hemoglobin content and components of the antioxidant defenses (superoxide dismutase (SOD) activity and ascorbic acid concentration). Furthermore, a possible protective effect of meso-2,3-dimercaptosuccinic acid (DMSA) and diphenyl diselenide (PhSe)2 are studied. The results demonstrated inhibition of delta-ALA-D and SOD activities, reduction in ascorbic acid, increase of lipid peroxidation induced by cadmium, indicating testes damage. DMSA (400 micromol/Kg) and (PhSe)2 (100 micromol/Kg) protected inhibitory effect of 2.5 mg/kg CdCl2 on delta-ALA-D and restored the increase of TBARS levels. Otherwise, (PhSe)2 treatment was effective in reducing the increase of TBARS levels induced by 5 mg/kg CdCl2, whereas DMSA and (PhSe)2, in combination, were ineffective in reducing TBARS level. However, these compounds alone or in combination, were unable to protect SOD activity and to improve ascorbic acid levels near to the normal value. The use of combined therapy (DMSA plus (PhSe)2) not proved be better than the monotherapy, in improving toxicological parameters evaluated in this model of testicular damage induced by cadmium.

Enzymes for heme biosynthesis are found in both the mitochondrion and plastid of the malaria parasite Plasmodium falciparum.

All eight enzymes required for de novo heme biosynthesis have been predicted from the nuclear genome of the human malaria parasite Plasmodium falciparum. We have studied the subcellular localization of three of these using a GFP reporter in live transfected parasites. The first enzyme in the pathway delta-aminolevulinic acid synthase (ALAS) is targeted to the mitochondrion, but the next two enzymes porphobilinogen synthase (PBGS) and hydroxymethylbilane synthase (HMBS) are targeted to the plastid. An enzymatically active recombinant version of PBGS from P. falciparum was over-expressed and its activity found to be stimulated by Mg2+ (and enhanced by Mn2+) but not by Zn2+. A hypothetical scheme for the exchange of intermediates in heme biosynthesis between the mitochondrion and plastid organelle, as well as organelle attachment is discussed.

Delta-aminolevulinic acid dehydratase activity in the general population of southern Minas Gerais, Brazil.

Blood samples were collected from 113 subjects (56 males and 57 females) living in the district of Alfenas, in southern Minas Gerais state, Brazil, to establish reference values for delta-aminolevulinic acid dehydratase activity (ALA-D, EC 4.2.1.24). The state of health of the population was confirmed by hematological and biochemical parameters analyzed in blood and urine samples. ALA-D determination was performed according to the Berlin & Schaller spectrophotometric method. Distribution may be regarded as according to normal distribution and reference values obtained, in micromol x min(-1) x L(-1) erythrocytes, were: mean (+/- SD) = 54.5 (+/- 9.8); 95% confidence interval = 52.7-56.4; lower reference value (mean-2 SD) = 34.9. Mean ALA-D activity was higher than any other published elsewhere and the reference values established are useful as a baseline for evaluating ALA-D activity when monitoring persons exposed to lead. Age, gender, drinking, or smoking did not significantly alter (Student t-test, p < or = 0.05) the reference values for ALA-D.

Biomarkers of lead exposure.

Biomarkers of exposure, effect, and susceptibility are reviewed in relation to lead exposure. Of the biomarkers of lead exposure, blood lead (Pb-B), mainly red cell lead, is a representative of soft tissue lead, and most widely used as measures of body burden and absorbed (internal) doses of lead. Urine lead (Pb-U) as well as plasma lead (Pb-P) increases exponentially with increasing Pb-B under a steady-state situation and is a reflection of recent exposure. The amount of lead in plasma and urine (MPb-P and MPb-U) after administration of a chelating agent (e.g. CaEDTA) can be useful for biomarkers of internal exposure of lead, reflecting the mobilizable pool of lead which consists of mainly blood and soft tissue lead with only a small fraction derived from bones. The critical effects in bone marrow arise mainly from the interaction of lead with some enzymatic process responsible for heme synthesis. The effects can be used for the biomarkers of effects. They are the inhibition of delta-aminolevulinic acid dehydratase (ALAD) and the variation in some metabolite concentrations (e.g. delta-aminolevulinic acid in urine (ALA-U), blood (ALA-B) or plasma (ALA-P), coproporphyrin in urine (CP), zinc protoporphyrin (ZP) in blood). The activities of pyrimidine nucleotidase (P5'N) and nicotinamide adenine dinucleotide synthetase (NADS) in blood are also decreased in lead exposure, and nucleotide contents in blood is altered in lead exposure. These effects of lead on human can be also useful biomarkers of effect. The differences in levels of heme precursors between two types of ALAD genotypes might be attributable to those in the affinity of different ALAD isozymes to lead. ALAD1 homozygotes have higher levels of ZP and ALA in comparison with ALAD2 carriers at the high lead exposure, suggesting that ALAD1 homozygotes might be more susceptible for disturbance in heme biosynthesis by lead than ALAD2 carriers.

Trace metals and metalloenzymes in placenta after oral administration of lead acetate.

The present study was carried out to find the effects of Pb acetate (10-50 mg/kg body wt) after oral administration on: 1. The distribution of elements, such as Fe, Cu, Zn, and Mn; 2. The activity of 6-amino levulenic acid dehydratase (delta-ALAD) and alkaline phosphatase (PAP); and 3. On the level of reduced glutathione (GSH) in murine placenta. Pb toxicity expressed on a dry-wt basis was reflected in terms of deficiency of delta-ALAD and PAP and enhanced content of GSH. Analysis of trace elements following Pb exposure showed low levels of Mn and Cu. Although Fe composition of placenta remained within normal range with increasing load of endogeneous Pb, Zn decline was not consistent after oral feeding of Pb acetate. Deficiency of PAP after Pb exposure did not correlate with the endogeneous levels of Pb or Zn therein, but correlated with endogeneous levels of Mn. Placental deficiencies of Cu and Mn have been related to the disturbed placental functions by Pb accumulation.

Enhancement of aminolevulinic acid based photodynamic therapy by adriamycin.

This paper reports on studies that evaluate the interaction between delta-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) and adriamycin (ADM) in an animal model system. Two groups of mice bearing a transplantable mammary adenocarcinoma received ADM i.p. in a single dose of 5 mg (low dose) and 30 mg (high dose) per kg body weight. Sixteen or 40 h after administration of the drug, mice were sacrificed, tumours, livers and hearts were removed and porphyrins, enzyme activities and malondialdehyde content were determined. Tumour explants of ADM-treated mice were incubated with ALA and irradiated with an He-Ne laser. Re-implantation of these in vitro PDT-treated explants into test animals showed that inhibition of tumour growth was significantly enhanced by combined treatment when the low dose of ADM was used. There were no significant changes in porphyrin content, ALA dehydratase and porphobilinogenase activities in the tissues analyzed after ADM treatment as compared with control values. ADM toxicity is thought to be related to semiquinone free radical formation with subsequent generation of reactive oxygen species such as peroxide and hydroxyl radical. These species are considered to initiate lipid peroxidation (LPO) and cause DNA damage. In the case of low-dose treatment with ADM a significant increase in the LPO product, malondialdehyde, was observed after PDT whereas with the high-dose regimen no changes were observed. In the case of explants of (non-irradiated) cardiac tissue malondialdehyde production was also found to be dependent on the dose and time of administration of adriamycin. In our in vivo/in vitro model system we have shown that pre-treatment with ADM increased the cytotoxicity of ALA-PDT at a dosage level of ADM which did not raise LPO levels in heart tissue. The mechanism of this effect has not been clearly elucidated but our data suggest that the observed enhancement of PDT may be attributed in part to the weakening of cellular defence mechanisms by the pre-treatment involving free radical generation by ADM.

Abnormalities of heme biosynthesis in experimental acute renal failure.

Several abnormalities of porphyrin metabolism have been described in patients with end-stage renal failure. Because the heme biosynthetic pathway in acute renal failure has not been studied hitherto, an experimental model was therefore induced in 30 dogs by ligation and transection of both ureters. Forty-eight h after this procedure, anemia and uremia developed, erythrocyte aminolevulinate dehydratase activity decreased, and plasma porphyrins increased in these 30 dogs, whereas seven sham-operated animals did not exhibit any alteration of these parameters. Uremic plasma showed a capacity to inhibit aminolevulinate dehydratase activity (mean, 11.1 +/- 5.8%) when incubated in vitro with erythrocytes from healthy dogs. Such findings are similar to those reported in uremic patients on hemodialysis or on continuous ambulatory peritoneal dialysis. Twenty-three of the 30 animals underwent a hemodialysis session (180 min) 48 h after ureteral ligation, using a polyacrylonitrile membrane dialyzer. In addition to reducing serum creatinine and urea levels, this procedure significantly reduced plasma porphyrin values. However, the activity of erythrocyte aminolevulinate dehydratase and the plasma capacity to inhibit this enzyme were not modified after the hemodialysis session. This results described here show that some of the abnormalities of heme biosynthesis described in chronic renal failure are detected early in an experimental model of acute renal failure. This study also confirms that, although most plasma porphyrins circulate bound to proteins, hemodialysis may reduce levels of plasma porphyrins when a high permeability membrane is used.

Indices of lead-exposure in blood and urine of lead-exposed workers and concentrations of major and trace elements and activities of SOD, GSH-Px and catalase in their blood.

Seventy male factory workers were studied. The lead concentrations in their blood (Pb-B) were 16.55 +/- 11.53 micrograms/100 ml (range 1.5 to 50.2 micrograms/100 ml). The subjects were divided into three groups according to Pb-B (in microgram/100 ml): group A, Pb-B < or = 10 (n = 22); group B, 10 < Pb-B < or = 20 (n = 30); group C, Pb-B > 20 (n = 18). The mean +/- S.D. in each group was 5.57 +/- 2.53, 15.02 +/- 2.75, and 32.52 +/- 9.49 micrograms/100 ml, respectively. Pb in plasma was 0.011 +/- 0.010, 0.017 +/- 0.033, and 0.021 +/- 0.021 microgram/liter, and Pb in the RBC was 0.281 +/- 0.246, 0.701 +/- 0.325, and 1.626 +/- 0.861 micrograms/g Hb, respectively. In addition to Pb concentration, the concentrations of 34 elements in the plasma or in the RBC were determined. Se concentrations in RBC in each group were 0.618 +/- 0.139, 0.670 +/- 0.207, and 0.728 +/- 0.200 microgram/g Hb, and the mean values were significantly different between groups A and C (p < 0.05). For Se concentration in plasma, the mean +/- S.D. in each group was 0.132 +/- 0.035, 0.130 +/- 0.031, and 0.126 +/- 0.021 microgram/ml, respectively, and there was no significant difference between groups. On the other hand, when the activities of total SOD, Mn-SOD, Cu, Zn-SOD, and catalase in the plasma and the activities of GSH-Px both in the plasma and in the RBC were assayed, some differences were found. The activities in GSH-Px in RBC were 17.19 +/- 5.03, 17.59 +/- 3.95, and 15.25 +/- 3.18 mumol/g Hb/min, and those in plasma were 0.069 +/- 0.032, 0.081 +/- 0.023, and 0.080 +/- 0.028 mumol/ml/min. In group C, GSH-Px activity was lower in the RBC and higher in the plasma than those in group A, and it was observed that the Se concentration was higher in RBC, and that there was no remarkable change in the plasma. Catalase activity in group C was 3.58 +/- 0.81 mgH2O2/ml/30 min, which was significantly higher than that in group A (2.81 +/- 0.90 mgH2O2/ml/30 min). Further investigation is necessary in order to explain the above results. The regular indices used for evaluating lead exposure, showed significant correlations with Pb-B: r = -0.786 vs delta-Aminolevulinic acid (ALA) dehydratase activity in blood, r = 0.927 vs. inhibition rate, and r = 0.339 vs. ALA in urine.

Lead poisoning associated with the use of Ayurvedic metal-mineral tonics.

OBJECTIVE: The aim of this study was to confirm the connection between lead poisoning and the use of traditional Ayurvedic metal mineral tonics. METHODS: The study group comprised 29 subjects (26 adults and three children) who had previously taken Ayurvedic metal mineral tonics. All subjects were tested for lead absorption by blood lead, erythrocyte delta-aminolevulinic acid dehydratase activity and erythrocyte protoporphyrin. RESULTS: Eighteen samples of Ayurvedic preparations were obtained from 15 subjects and analyzed for lead content. Five adult subjects with established lead poisoning received chelation therapy. In Ayurvedic preparations a wide range of lead content was found (0.9-72,990 micrograms Pb/g; 0.35-29,900 micrograms Pb/capsule or tablet). The blood lead, erythrocyte delta-aminolevulinic acid dehydratase and erythrocyte protoporphyrin of the subjects, grouped according to the remedies used, correlated with the lead content in the preparations (p < 0.001). Chelation therapy was successful in normalization of laboratory findings and clinical recovery. CONCLUSION: Ayurvedic metal-mineral tonics are again identified as a potential source of high lead. The import of such tonics should be strictly controlled.

Zinc aminolevulinic acid dehydratase reactivation index as a tool for diagnosis of lead exposure.

The correlation between blood lead level (BLL), delta-aminolevulinate dehydratase (ALA-D) activity, and other common biochemical parameters used to assess a plumbism diagnosis have been carefully analyzed, with the aim of correctly interpreting the data handled in the laboratory. No correlation was observed between BLL and free erythrocyte porphyrins. In the case of ALA-D or Zn-reactivated ALA-D despite the direct correlation with BLL, the curve follows a potential or a logarithmic line, which is not the best to calculate BLL. The so-called Zn-ALA-D-reactivation index (iZn) has been defined as the ratio between the activity of Zn-reactivated ALA-D and the activity of ALA-D. The plot of BLL against the iZn revealed a very good linear relationship which allows an estimate of BLL with reasonable accuracy within a very wide range.

Valores referenciales de la enzima delta aminolevulínico dehidratasa eritrocitaria en Jujuy: influencia de la altitud / Delta aminolevulinic acid dehydratase enzime reference's values in blood in Jujuy: high over sea level influence

La actividad de la enzima ALAD en sangre, es uno de los parámetros más útiles para evaluar la exposición al plomo, por su sensibilidad y especificidad a los niveles de plomo sanguíneo y de los depósitos biológicamente activos. El estudio se orientó a obtener valores de referencia para esta enzima en la Provincia de Jujuy, y comprobar si están condicionados por la altitud, ya que Jujuy presenta un relieve con amplias variaciones altimétricas, entre 600 y 4.500 metros sobre el nivel del mar. Se estudiaron muestras de sangre de poblaciones de la Puna (3.500 metros de altitud), de la Quebrada de Humahuaca (2.800 metros) y valle de San Salvador de Jujuy (1.300 metros). Si bien se hallaron mayores niveles de ALAD (Método Europeo Estandarizado) en la Puna, se interpretó como una respuesta de los moradores de una zona libre de contaminación plúmbica, cuyas estrategias de supervivencia son diferentes a las de otras zonas. Deben considerarse valores de referencia únicos para la Provincia, independientemente de la altitud en que residan sus habitantes. Se establecen valores de referencia y valores límites normales para varones, mujeres y población general

Valores referenciales de la enzima delta aminolevulínico dehidratasa eritrocitaria en Jujuy: influencia de la altitud / Delta aminolevulinic acid dehydratase enzime references values in blood in Jujuy: high over sea level influence

La actividad de la enzima ALAD en sangre, es uno de los parámetros más útiles para evaluar la exposición al plomo, por su sensibilidad y especificidad a los niveles de plomo sanguíneo y de los depósitos biológicamente activos. El estudio se orientó a obtener valores de referencia para esta enzima en la Provincia de Jujuy, y comprobar si están condicionados por la altitud, ya que Jujuy presenta un relieve con amplias variaciones altimétricas, entre 600 y 4.500 metros sobre el nivel del mar. Se estudiaron muestras de sangre de poblaciones de la Puna (3.500 metros de altitud), de la Quebrada de Humahuaca (2.800 metros) y valle de San Salvador de Jujuy (1.300 metros). Si bien se hallaron mayores niveles de ALAD (Método Europeo Estandarizado) en la Puna, se interpretó como una respuesta de los moradores de una zona libre de contaminación plúmbica, cuyas estrategias de supervivencia son diferentes a las de otras zonas. Deben considerarse valores de referencia únicos para la Provincia, independientemente de la altitud en que residan sus habitantes. Se establecen valores de referencia y valores límites normales para varones, mujeres y población general (AU)

Cloning and sequencing of a previously unidentified gene that is involved in the biosynthesis of heme in Escherichia coli.

We have isolated a number of porphyrin (Por)-synthesis mutants as light-resistant revertants of a light-sensitive strain delta visA (hemH) of Escherichia coli that accumulates protoPor IX in the cell. Among such mutants, we found a double mutant (H103) with mutations in hemA and in a new gene downstream of hemA. This new gene, designated hemK, was located at 27 min on the linkage map of the E. coli chromosome. By nucleotide (nt) sequencing, it was demonstrated that hemK forms part of the hemA-prfA-hemK operon and encodes 225 amino acids that show no significant homology to any protein in the standard databases. The mutant strain H103 formed small colonies and showed no catalase activity even in the presence of 5-aminolevulinic acid (ALA), indicating its inability to catalyze a step in the biosynthesis of heme from ALA. An extract of H103 cells has readily detectable ALA dehydratase and porphobilinogen deaminase activities. H103 cells carrying a plasmid that included only hemA as an insert accumulated protoPor and coproPor, but showed no sensitivity to light, a result that suggests that it may be deficient in protoporphyrinogen oxidase activity.

Tissue distribution of succinylacetone in the rat in vivo: a possible basis for neurotoxicity in hereditary infantile tyrosinemia.

Neurologic dysfunction is a significant component of hereditary infantile tyrosinemia, an autosomal recessive disorder of man. The specific enzyme defect leads to endogenous production of the biochemical marker compound, succinylacetone (SA). Earlier study of the role which SA plays in generation of the renal Fanconi syndrome, also associated with this disorder, led to speculation that SA might also have neurotoxic effects. Thus, we have studied the distribution and impact on heme metabolism of SA in brain, liver and kidney from rats treated in vivo. Our results show far greater retention of SA in brain and kidney than in liver, by a ratio of approx. 3:1. Delta-aminolevulinate dehydratase (ALAD) was reduced to less than 10% of control activity in all three tissues after three daily injections; after a 7-day recovery, activity was regained at different rates in the three tissues. Total heme content of each tissue showed a steady decline beyond the treatment period, the most marked reduction being found in kidney. Porphyrin intermediates, heme oxygenase activity and cytochrome P-450 content evidenced varying responses to SA exposure which differed from tissue to tissue. Our results show that brain tissue sequesters SA and that heme biosynthesis in brain, as distinct from liver and kidney, is adversely affected. Such effects could result in impaired oxidative metabolism in brain, producing the CNS manifestations of tyrosinemia.