Ornithine Carbamyl Transferase Research Articles

Bacterial-like energy metabolism in the amitochondriate protozoon Hexamita inflata.

Hexamita inflata is an amitochondriate flagellated protozoon which inhabits O(2)-limited environments. With the aid of 1H NMR spectroscopy, analysis of the metabolic fluxes in H. inflata grown in complex media under limited O(2) was performed. Almost complete carbon recovery from maltose (the principle carbohydrate source in the medium) catabolism was calculated from the measured increase in concentration of ethanol, alanine, acetate and lactate (and estimated CO(2) production). Difference spectra and amino acid analysis also identified changes in concentration of metabolites belonging to the arginine dihydrolase (ADH) pathway. The enzymes of the ADH pathway were detected in extracts with the following activities (in nmoles min(-1) x (mg of protein) x (-1)): arginine deiminase, 3.30; catabolic ornithine carbamyltransferase (OCT), 1.3; anabolic OCT, 93.0; and carbamate kinase, 1829. The organism metabolized the ornithine produced from catabolic OCT activity to putrescine via ornithine decarboxylase (ODC). The polyamines, spermidine and spermine, were formed by the sequential addition of the aminopropyl group of decarboxylated S-adenosyl-L-methionine (SAM) by the respective polyamine synthases. In addition, asparaginase activity was confirmed in H. inflata, catalysing the deamination of asparagine generating aspartate and ammonia. This study also indicates that, as with other amitochondriate protozoa and some bacteria, the ADH pathway significantly contributes to the energy yield of the cell, particularly under O(2)-limited conditions.

1082 Designer cells for a bioartificial liver-restoring ornithine carbamyl transferase (OTC) activity to HEP G2 cells by transfection and 3-dimensional culture restores urea synthesis to levels

1082 Designer cells for a bioartificial liver-restoring ornithine carbamyl transferase (OTC) activity to HEP G2 cells by transfection and 3-dimensional culture restores urea synthesis to levels

Isolation and molecular analysis of the gene cluster for the arginine deiminase system from Streptococcus gordonii DL1.

The arginine deiminase (AD) system (ADS) is one of two major ammonia-generating pathways in the oral cavity that play important roles in oral biofilm pH homeostasis and oral biofilm ecology. To initiate a study of the Streptococcus gordonii ADS, the ADS gene cluster was isolated from subgenomic DNA libraries of S. gordonii DL1 by using an arcB-specific probe. Nucleotide sequence analysis revealed six open reading frames (ORFs) that were arranged contiguously; the first five ORFs were transcribed in the same direction, as an apparent operon, and the sixth was transcribed in the opposite direction. The ORFs were found to share significant homologies and to correspond closely in molecular mass to previously characterized arc genes; thus, they were designated arcA (AD), arcB (ornithine carbamyltransferase), arcC (carbamate kinase), arcD (arginine-ornithine antiporter), arcT (dipeptidase), and arcR (regulator). A putative sigma(70) promoter (ParcA [TTGTGT-N(19)-TAGAAT]) was mapped 5' to arcA by primer extension, and the expression of ParcA was shown to be inducible by arginine and repressible by glucose, in agreement with AD specific activities measured in the wild-type strain. To investigate the function of ArcR in the differential expression of the arc operon, arcR was insertionally inactivated by a KM resistance marker flanked by T4 transcription/translation termination signals, and the expression of ParcA was monitored by primer extension in the wild-type and ArcR-deficient strains. Lower levels of arcA expression, as well as lower levels of AD activity, were consistently observed in the ArcR-deficient strain compared to wild-type cells, regardless of the growth conditions. Thus, ArcR is a transcriptional activator that is required for induction and optimal expression of the S. gordonii ADS gene cluster.

Serum Mineral and Haematobiochemical Profile of Microfilariae Infected Cattle in India: Its Effects on Production and Therapy

A survey was under taken of six district of Northern India viz. Bareilly, Pilibhit, Udham Singh Nagar, Nainital, Almora and Rampur. The age, breed, sex and physiological status recorded. A total number of 854 cattle examined out of which lactating (274 cases), non lactating (302 cases) heifers (128 cases), calves (82 cases) and adult male (68 cases) were examined. An incidence of 4.92 percent (42) of microfilarisis was recorded. The highest prevalence was observed in Rudrapur District of Udham Singh Nagar (33.33%, 4/12), followed by Lalkaun in Nanital District (21.74%, 10/46), Rampur (12.50%, 2/16), Bareilly (8.16%, 8/98) and Pilibhit (1.22%, 1/82). No infection was observed in Almora region. Amongst 854 cattle of different group incidence was highest in adult male (12.20%, 10/82), followed by non lactating (3.82%, 12/314) and lactating (2.70%, 2/74), (7.64%, 12/157) was found in Heifers. For haemeto-biochemical, serum minerals estimations and therapeutic study 32 animals suffering from filariasis and 18 healthy animals were taken. 16 animals were treated with ivermectin @200 µg/kg body weight. Effect of this disease on production has also been estimated for which body weight and milk production was observed. The main clinical manifestations observed were anaemia, loss of appetite, debility, oedematous swelling especially in the abdominal region, increased heart rate, and respiration rate. Haematological changes indicated decrease in hemoglobin, total erythrocyte count, packed cell volume, erthrocyte fragility and neutrophil, whereas there was significant increase in erythrocytes sedimentation rate (ESR), total leukocyte count (TLC), lymphocyte and eosinophils. Biochemical changes showed significant reduction in the values of serum albumin, A : G ratio, where as there was significant increase in blood glucose, blood urea nitrogen (BUN), globulin, total lipid, total cholesterol, phospholipids, serum bilirubin. Serum mineral profile also altered markedly, which indicate a significant decrease in Ca, Cu, Fe, Zn, and Mn with increase value of Na and Cl. There was no significant change in P and K values. Enzyme pattern in micro filaria infected animal indicated increased level of AST, ALT, alkaline phosphatase, ornithine carbamyl transferase, sorbitol dehydrogenase, glutamate dehydrogenase, isocitric dehydrogenase and lactate dehydrogenase. In blood gas values and acid/base balance, there was an increase in PVCo2 and PVo2. It has been observed that microfilaria infected cattle showed decrease in body weight and milk production. Animal treated with ivermectin showed the return of these above values toward normalcy. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 3 : 357-365)

Development of a bienzyme reactor sensor system for the determination of ornithine

A bienzyme reactor sensor system with amperometric detection was developed for the determination of ornithine. The system based on the immobilized enzymes (ornithine carbamyl transferase and pyruvate oxidase) consisted of a buffer tank, a peristaltic pump, an enzyme reactor, an oxygen electrode and a recorder. Then, 0.1 M MOPS buffer, containing pyruvic acid (0.5 mM) and carbamyl phosphate (0.5 mM), was continuously transferred into the system at 35 °C. Phosphate ion was formed enzymatically by transformation of ornithine in the presence of carbamyl phosphate. Pyruvate oxidase is activated by the presence of phosphate. Therefore, ornithine was determined from the oxygen consumed upon oxidation of pyruvic acid catalyzed by pyruvate oxidase in the presence of phosphate ion. The limit of detection was 0.05 mM and the response was linear to 3 mM ( R 2=0.9905). The variation coefficients were 4.9 ( n=15) and 3.9% ( n=15) for 1.1 and 3.0 mM standard ornithine, respectively. Good comparative results ( R 2=0.9238) were observed between ornithine contents in prawn muscle determined by the proposed system and by the HPLC. One assay was completed within 4 min. The immobilized enzymes were stable for 2 months at 4 °C and more than 150 samples could be continually determined using this enzyme reactor.

Mouse CLK-1 Is Imported into Mitochondria by an Unusual Process That Requires a Leader Sequence but No Membrane Potential

clk-1 has been identified and characterized in the nematode Caenorhabditis elegans as a gene that affects the rates, regularity, and synchrony of physiological processes. The CLK-1 protein is mitochondrial and is required for ubiquinone biosynthesis in yeast and in worms, but its biochemical function remains unclear. We have studied the expression of murine mclk1 in a variety of tissues, and we find that the pattern of mclk1 mRNA accumulation closely resembles that of mitochondrial genes involved in oxidative phosphorylation. The pattern of protein accumulation, however, is sharply distinct in some tissues; mCLK1 appears relatively enriched in the gut and depleted in the nervous tissue. We also show that mCLK1 is synthesized as a preprotein that is imported into the mitochondrial matrix, where a leader sequence is cleaved off and the protein becomes loosely associated with the inner membrane. However, in contrast to all known mitochondrial proteins that contain a cleavable pre-sequence, the import of mCLK1 does not require a mitochondrial membrane potential.

Influence of amodiaquine treatment on microsomal lipid peroxidation and antioxidant defense systems of rats.

The effects of single and multiple doses amodiaquine treatment on enzymatic and non-enzymatic antioxidant profiles and hepatic microsomal lipid peroxidation were investigated in rats. Treatment of rats with 10 mg/kg (single dose) amodiaquine resulted in 10% and 63% increases, respectively in the activities of liver superoxide dismutase and glutathione peroxidase (P<0.01), while the activity of liver catalase was significantly reduced by 26% compared to control. The levels of serum vitamins A, C and beta-carotene were lowered following amodiaquine treatment. Following multiple dose (10 mg/kg for 4 consecutive days) amodiaquine treatment, activities of superoxide dismutase and glutathione peroxidase were increased by 30% and 133% respectively while catalase activity was decreased by 45%. Similarly, serum vitamins A, C and beta-carotene levels were markedly decreased. In the single dose study, the levels of malondialdehyde and the activity of glutathione S-transferase were increased by 15% and 44% respectively while the reduced glutathione was decreased by 25% compared to control. Malondialdehyde level was highly increased (P<0.001) by 71% following multiple amodiaquine treatment. Reduced glutathione was decreased by 55% and unlike in the single dose study, activity of glutathione S-transferase was decreased by 60% compared to control. The activities of serum aspartate amino transferase, alanine amino transferase, ornithine carbamyl transferase and gamma-glutamyl transferase were significantly increased by both single and multiple doses of amodiaquine treatment (P<0.01). The alteration in enzymatic and non-enzymatic antioxidant defense system, increase in lipid peroxidation and increase in the activities of serum enzymes following amodiaquine treatment suggests damage to the liver and could subject the organ to further oxidative stress. The relevance of this to continuous exposure to amodiaquine therapy should be considered.

Chemoprevention of 2-acetylaminofluorene-induced hepatotoxicity and lipid peroxidation in rats by kolaviron—A Garcinia kola seed extract

The effect of kolaviron, a mixture of Garcinia biflavonoid 1 (GB1), Garcinia biflavonoid 2 (GB2) and kolaflavanone, used in the treatment of various ailments in southern Nigeria on hepatotoxicity and lipid peroxidation induced by 2-acetylaminofluorene (2-AAF) in rats was investigated. The ability of butylated hydroxyanisole (BHA) to attenuate the toxic effect of 2-AAF was also examined. Kolaviron administered orally to rats at a dose of 100 mg/kg body weight twice a day for 1 week before challenge with 2-AAF (200 mg/kg feed) and continuously for 3 weeks at a single dose of 200 mg/kg body weight reversed the 2-AAF-mediated decrease in final body weight and relative organ weights, especially the liver. BHA was administered at a dose of 7.5 g/kg feed to the animals for 4 weeks. The extract decreased significantly the 2-AAF-mediated increase in the activity of aspartate aminotransferase, alanine aminotransferase, γ-glutamyl transferase and ornithine carbamyl transferase by 58%, 62%, 60% and 67%, respectively. BHA elicited respectively 55%, 63%, 57% and 65% reduction in the 2-AAF induced-increase in the activities of these enzymes. Histological examination of the liver slices correlated with the changes in serum enzyme alterations. Similarly, kolaviron decreased the 2-AAF reduction of 5′-nucleotidase and glucose-6-phosphatase activities by 63% and 60%, respectively while BHA elicited 59% and 61% decrease in the activities of these enzymes. Simultaneous administration of kolaviron with 2-AAF inhibited microsomal lipid peroxidation as assessed by the thiobarbituric acid reacting substances (TBARS) formation by 66%. BHA produced a 64% reduction in TBARS formation. In the present study, kolaviron appears to act as an in vivo natural antioxidant and an effective hepatoprotective agent and is as effective as BHA.

Retrospective evaluation of serum ornithine carbamyltransferase activity as an index of hepatotoxicity in toxicological studies with rats

The sensitivity of elevated serum ornithine carbamyltransferase (OCT) as an index of hepatotoxicity in rats was assessed in different studies conducted over a number of years and originally designed to examine the toxicity or carcinogenicity of a variety of test chemicals and diets. Changes in serum OCT activities were compared with the more widely used clinical endpoints, alanine aminotranserase (ALT) and aspartate aminotransferase (AST). In the first study, rats received a single oral dose of the hepatotoxic and hepatocarcinogenic fungal toxin aflatoxin B 1 (AFB 1). The increase in enzyme levels between control and AFB 1-treated rats was greater for serum OCT than for ALT or AST. This response was similar to the changes in serum enzyme levels in studies where rats ingested a hepatotoxic and hepatocarcinogenic choline deficient (CD) diet. When rats were exposed to the hepatotoxic and nephrotoxic fungal toxin fumonisin B 1 (FB 1) by intraperitoneal injection for 6 days, serum AST and ALT were significantly elevated above control levels while OCT was unaffected. The peroxisome proliferator ciprofibrate caused elevated ALT and AST but not OCT at week 52 of dietary exposure, after the development of liver nodules and tumours. Of the two liver-specific enzymes examined in all of the studies, ALT was more consistently predictive of hepatotoxicity than OCT.

The allopurinol load test lacks specificity for primary urea cycle defects but may indicate unrecognized mitochondrial disease.

Thirty-three children ranging from 2 weeks to 12 years of age were selected for allopurinol loading, 16 on the basis of an increased urinary ourotate excretion detected by routine organic acid analysis (group A), and 17 for clinical reasons suggesting a urea cycle defect (group B). The allopurinol load test proved positive in 13 of 16 patients from group A, mean peak orotate 64.0 mumol/mmol creatinine (upper limit of reference range, 13.2) and 11 of 17 patients from group B, mean peak orotate 41.0 mumol/mmol creatinine (upper limit of reference range, 13.2). Thorough investigation of these patients including urinary and plasma amino acid analysis and, in 17 cases, liver biopsy for histology and measurement of ornithine carbamyltransferase (OCT) and carbamyl-phosphate synthetase (CPS) activity failed to identify any evidence of a urea cycle disorder. However, muscle biopsies performed in 11 patients showed some evidence of mitochondrial disease in four cases, two defined on the basis of reduced respiratory chain enzyme activity and two on the basis of mtDNA abnormalities. These findings indicate that an increased excretion of orotate in sick children may not be uncommon and that a positive allopurinol load test result may not indicate a specific inherited urea cycle defect. In addition, these results raise the interesting possibility that defective ureagenesis may be a feature of mitochondrial disease in some individuals.

Buffer effect on the kinetics of ornithine carbamyl transferase by HPLC.

A kinetic study of ornithine carbamyl transferase (OCT) from Streptococcus faecalis has been carried out, employing a new HPLC method based on the direct determination of citrulline. A different kinetic pattern was observed in tris(hydroxymethyl)-aminomethane (TRIS) and triethanolamine (TEA) buffers: a ping-pong or an ordered sequential mechanism are suggested, respectively. The inhibition of Tris buffer on OCT reaction has also been demonstrated. The inhibition of Tris buffer on OCT reaction has also been demonstrated.

Development of ornithine biosensor and application to estimation of prawn freshness

The ornithine biosensor based on the immobilized enzymes (ornithine carbamyl transferase, nucleoside phosphorylase and xanthine oxidase) consisted of an oxygen electrode, flow cell, peristaltic pump, recorder and buffer tank. The optimum conditions for the sensor were as follows: pH 8.2, temperature 32°C, flow rate 0.2 ml/min, sample volume 50 μl and transfer solution 0.1 M Tris-HCI buffer solution. A good correlation was obtained between ornithine contents in kuruma prawn muscle which were determined by the biosensor and those by high performance liquid chromatography (HPLC). From these results, the freshness of prawn can be estimated by the determination of ornithine with the proposed sensor system.

A novel approach to practical enzymology teaching: a conductimetric investigation of arginase, inorganic pyrophosphatase, aliphatic esterase, ornithine carbamyl transferase and argininosuccinate lyase activities from mammalian liver

Kinetic conductivity measurement, run as a microcomputer-controlled workstation with eight independent reaction cells, is shown here to be a simple, cost-effective method for assaying enzymes. The technique is demonstrated with enzymes that can be used as markers for the major subcellular compartments of hepatocytes as a one-day student laboratory class with great potential for variation and development. The method is virtually unknown in enzymology, but could be envisaged as standard apparatus for all biochemical laboratories and teaching classes.

Protein Import into Subsarcolemmal and Intermyofibrillar Skeletal Muscle Mitochondria: DIFFERENTIAL IMPORT REGULATION IN DISTINCT SUBCELLULAR REGIONS

To date, no studies have described the import of proteins in mitochondria obtained from skeletal muscle. In this tissue, mitochondria consist of the functionally and biochemically distinct intermyofibrillar (IMF) and subsarcolemmal (SS) subfractions, which are localized in specialized cellular compartments. This mitochondrial heterogeneity in muscle could be due, in part, to differential rates of protein import. To evaluate this possibility, the import of precursor malate dehydrogenase and ornithine carbamyltransferase proteins was investigated in isolated IMF and SS mitochondria in vitro. Import of these was 3-4-fold greater in IMF compared with SS mitochondria as a function of time. This could account for the higher malate dehydrogenase enzyme activity in IMF mitochondria. Divergent import rates in IMF and SS mitochondria likely result from a differential reliance on various components of the import pathway. SS mitochondria possess a greater content of the molecular chaperones hsp60 and Grp75, yet import is lower than in IMF mitochondria. On the other hand, adriamycin inhibition studies illustrated a greater reliance on acidic phospholipids (i.e. cardiolipin) for the import process in SS mitochondria. Matrix ATP levels were 3-fold higher in IMF mitochondria, but experiments in which ATP depletion was performed with atractyloside and oligomycin illustrated a dissociation between import rates and levels of ATP. In contrast, a close relationship was found between the rate of ATP production (i.e. mitochondrial respiration) and protein import. When respiratory rates in IMF and SS mitochondria were equalized, import rates in both subfractions were similar. These data indicate that 1) import rates are more closely related to the rate of ATP production than the steady state ATP level, 2) import into IMF and SS mitochondrial subfractions is regulated differently, and 3) mitochondrial heterogeneity within a cell type can be due to differences in the rates of protein import, suggesting that this step is a potentially regulatable event in determining the final mitochondrial phenotype.

The contribution of the arginine dihydrolase pathway to energy metabolism by Trichomonas vaginalis

The enzymes of the arginine dihydrolase pathway were measured in Trichomonas vaginalis hydrogenosome-deficient lines MR-5 and MR-100, and the parent strain TV 10-02. The activities and substrate affinities of arginine deiminase, carbamate kinase and ornithine decarboxylase were similar for the hydrogenosome-deficient lines and the parent TV 10-02. The activity of catabolic ornithine carbamyltransferase, however, was found to be 5–7-fold elevated in the hydrogenosome-deficient lines; the apparent Km for citrulline was similar for all of the lines. Putrescine biosynthesis by the hydrogenosome-deficient cell lines was found to be significantly higher than the parent. Incubation of strain MR-100 with U-[14C]-arginine resulted in a 5-fold greater amount of 14CO2 liberated compared to the parent strain TV 10-02. Inclusion of the ornithine decarboxylase inhibitor difluoromethylornithine in these incubations reduced the CO2 production of strain TV 10-02 by 42%, but only inhibited the MR-100 strain by 14.5%, indicative that the majority of the CO2 liberated from arginine by this strain is derived from the elevated activity of ornithine carbamyltransferase. Despite the increased flow through the arginine dihydrolase pathway, the energy gain to the parasite is ∼10% of that from glucose, thus, under the growth conditions used in this study carbohydrate metabolism provides the bulk of the ATP for the parasite.

Formation of Paramagnetic Chromium in Liver of Mice Treated with Dichromate (VI)

The formation of paramagnetic chromium in the liver of male mice dosed with K2Cr2O7 (10, 20, and 40 mg Cr/kg) by a single ip injection was investigated by electron spin resonance (ESR) spectrometry. Both Cr(V) and Cr(III) complexes were detected in the mice livers at 15 min to 12 hr after Cr(VI) injection. The time course (15 min-12 hr) for the formation of paramagnetic Cr revealed that the hepatic levels of Cr(V) complexes decreased quickly during the first hour but decreased more slowly over the next 11 hr. However, in contrast to Cr(V), Cr(III) complexes appeared to persist for 12 hr after Cr(VI) treatment based on figures of Cr(III) signal. Thus, Cr(III) may be the ultimate form following reduction of Cr(VI) in liver. The total Cr content in liver of mice dosed with dichromate was also increased in a dose-dependent fashion (10-40 mg Cr/kg). However, Cr content in liver remained at similar levels for 15 min-6 hr, and slightly decreased at 12 hr after Cr(VI) injection. Under the same experimental conditions, hepatotoxicity, as estimated by the increase of serum ornithine carbamyl transferase activity, appeared at 3 hr after 20 and 40 mg Cr/kg of Cr(VI) injection, while 10 mg Cr/kg of Cr(VI) produced no hepatotoxicity even at 12 hr. Predosing with phenobarbital, which increased the hepatic levels of cytochrome P450, resulted in a decrease of the levels of Cr(V) and in a small increase of Cr content, without affecting Cr(VI) hepatotoxicity. On the other hand, pretreatment with buthionine sulfoximine, which depleted hepatic glutathione (GSH) levels, caused a decrease of Cr(VI) hepatotoxicity, but the levels of Cr(V) and Cr in the liver remained unchanged. These results demonstrated that in vivo formation of paramagnetic Cr, in particular Cr(V), in liver of mice is clearly detected and quantified by ESR spectrometry and that hepatic levels of cytochrome P450 and GSH are associated with the induction of biological effects by Cr(VI) in liver in vivo. The results also suggested that the formation of Cr(V) was not the only mechanism involved in the induction of hepatotoxicity by Cr(VI) compounds.

Role of nitric oxide during carrageenan-sensitized endotoxin shock in mice

We have previously clarified that sensitization with a sulfated polygalactose, carrageenan (CAR), enhances endotoxin-induced tumor necrosis factor (TNF) production and lethality in mice. The present study was performed to examine the role of nitric oxide (NO) in CAR-sensitized septic mice with two different types of NO synthase (NOS) inhibitors, a non-selective inhibitor to NOS subtypes, N ω-nitro-L-arginine methyl ester (L-NAME), and a selective inhibitor to inducible NOS, aminoguanidine. Seven or eight-week-old male ddY mice were given 5 mg of CAR intraperitoneally as a primer. Then, 5 μg of lipopolysaccharide (LPS) was injected into the tail vein 16 hours later the pretreatment. Marked synthesis of NO was induced in CAR-sensitized mice, as indicated by the high plasma levels of the stable endproducts, NO 2 − NO 3 − peaking at 12 hr after the LPS challenge. The peak values at 12 hr after the LPS challenge were dependent on the dose of CAR with 1 to 5 mg, although the injection with 10 mg of CAR was adversely inhibited NO production compared with 5 mg of CAR. The LPS challenge was followed by either L-NAME (0.25, 0.5 or l mg) or aminoguanidine (1, 2 or 4 mg) in the septic mice sensitized with 5 mg of CAR. L-NAME reduced the plasma NO 2 − NO − level in a dose-dependent fashion, although it augmented liver injury, as measured by plasma levels of ornithine carbamyltransferase (OCT) and the LPS-induced lethality in a dose-dependent fashion. In contrast, aminoguanidine did not significantly deteriorate either liver injury or lethality in spite of the decrease of NO endproducts in a similar fashion to L-NAME. These findings suggest that the inhibition of constitutive NOS is detrimental and augments LPS-induced liver injury and subsequent lethality.

Role of cytochrome P450 in hepatotoxicity induced by di- and tributyltin compounds in mice.

The role of cytochrome P450 in the induction of hepatotoxicity by butyltin compounds such as tributyltin chloride (TBTC) and dibutyltin dichloride (DBTC) was investigated in vivo. The pretreatment of mice with SKF-525A, which decreased hepatic levels of cytochrome P450, suppressed TBTC-induced hepatotoxicity, as estimated by serum ornithine carbamyl transferase activity, whereas pretreatment with phenobarbital (PB), which increased the levels of cytochrome P450, enhanced the hepatotoxicity of TBTC. In the case of DBTC, PB pretreatment enhanced hepatotoxicity, while SKF-525A had no effect. Under these experimental conditions only PB pretreatment was found to increase hepatic levels of tin in mice treated with TBTC. These results suggest that hepatic metabolism of butyltin compounds by cytochrome P450 is more closely related to the induction of hepatotoxicity by TBTC than by DBTC. The active tin compounds formed during hepatic metabolism, which are responsible for induction of hepatotoxicity, will be discussed.

Effect of UV-B (302 nm) irradiation on isolated rat hepatocytes.

The present study aimed to evaluate the effect of UV-B irradiation on the functional integrity, and the metabolic and detoxifying capacity of isolated rat hepatocytes. Isolated rat hepatocytes were irradiated in various doses (400 Jm-2, 600 Jm-2, 800 Jm-2 and 1000 Jm-2). The cells were assayed for total lactate dehydrogenase, Na(+)-K(+)-ATPase, ornithine carbamyltransferase activity (OCT) and urea production capacity. Lactate dehydrogenase and Na(+)-K(+)-ATPase activity were significantly decreased in all four irradiated groups (P < 0.001), whereas viability, OCT and urea production capacity showed no alterations.

Subcellular localization of the enzymes of the arginine dihydrolase pathway in Trichomonas vaginalis and Tritrichomonas foetus.

The enzymes of the arginine dihydrolase pathway were demonstrated in Tritrichomonas foetus and their subcellular localization determined for both T. foetus and Trichomonas vaginalis. Ornithine carbamyltransferase (anabolic and catabolic activities), ornithine decarboxylase and carbamate kinase activity were localized predominately (56-80%) in the non sedimentable fraction of both species. A large proportion (35-40%) of the arginine deiminase was, however, recovered in the large granular fraction, and this distribution was unchanged by increasing the ionic strength of the buffer. Upon density gradient centrifugation the particles containing arginine deiminase activity had an isopycnic density of 1.09 g/ml in percoll, and separated from hydrogenosomes (1.18 g/ml) and lysosomes (1.12 g/ml). Arginine deiminase was also the only enzyme of the dihydrolase pathway which demonstrated latency upon treatment of the 1.09 g/ml fraction with non-ionic detergents. The results demonstrate the presence of the arginine dihydrolase pathway in T. foetus and indicate that at least a portion of the arginine deiminase in trichomonads is membrane associated.