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PubMed1979

Genetics and physiology of proline utilization in Saccharomyces cerevisiae: enzyme induction by proline.

Proline is converted to glutamate in the yeast Saccharomyces cerevisiae by the sequential action of two enzymes, proline oxidase and delta 1-pyrroline-5-carboxylate (P5C) dehydrogenase. The levels of these enzymes appear to be controlled by the amount of proline in the cell. The capacity to transport proline is greatest when the cell is grown on poor nitrogen sources, such as proline or urea. Mutants have been isolated which can no longer utilize proline as the sole source of nitrogen. Mutants in put1 are deficient in proline oxidase, and those in put2 lack P5C dehydrogenase. The put1 and put2 mutations are recessive, segregate 2:2 in tetrads, and appear to be unlinked to one another. Proline induces both proline oxidase and P5C dehydrogenase. The arginine-degradative pathway intersects the proline-degradative pathway at P5C. The P5C formed from the breakdown of arginine or ornithine can induce both proline-degradative enzymes by virtue of its conversion to proline.

Enzyme Induction↗
PubMed1978

Enzyme induction in the uremic liver.

Forty-five days after subtotal nephrectomy or sham-operation of male rats, microsomal enzymes were investigated in vitro. The activities (per milligram) of microsomal protein of two esterases and of two glucuronyltransferases were normal in the uremic rats. The mixed-function oxidation system had lower activities per milligram of protein than that in sham-operated controls. Due to a decrease of the microsomal protein content of the uremic liver, the activities of these enzymes were decreased when calculated for the whole liver. In contrast, the glucoronidation of phenolphthalein remained normal when related to the whole liver, due to an increased activity per mg of protein. Treatment with the plasticizer di-(2-ethylhexyl)-phthalate caused a significant increase of the liver wet weight, the microsomal protein content, and the activity per mg of protein for the demethylation of aminopyrine in subtotally nephrectomized rats but was without influence on the liver of sham-operated controls. It is concluded that uremia itself does not induce liver microsomal enzymes. The microsomal enzymes, however, remain inducible by foreign compounds even under uremic conditions.

Animals↗
PubMed1997

Early effects of CI-924 on hepatic peroxisome proliferation, microsomal enzyme induction, PCNA, and apoptosis in B6C3F1 mice and Wistar rats.

The lipid lowering agent 5,5'[[1,1'-biphenyl]-2,5-diylbis(oxy)]bis[2,2-dimethylpentanoic acid] (CI-924) is a peroxisome proliferator in rats and mice, but increased the incidence of hepatic tumors in mice only. Male and female B6C3F1 mice and albino Wistar rats were treated with CI-924 at doses of 0, 25 and 75 mg/kg for 1, 3, 7 and 28 days. Our aim was to identify species differences potentially related to tumorigenicity and to establish the time course of early events related to or associated with peroxisome proliferation. After 24 h of exposure to CI-924 in the diet there were increases in carnitine acyl transferase and CYP4A1 activity in mice at 25 and 75 mg/kg. In rats, carnitine acyl transferase activity was increased after 24 h and CYP4A1 activity increased after 3 days at 75 mg/kg. Acyl CoA oxidase activity was increased at both doses in male and female rats and mice by 3 days. In general the changes in enzyme activity were of greater magnitude in rats. In contrast to the rapid peroxisome proliferation, increases in the amount of PCNA were observed in CI-924 treated rats and mice at later times after administration and only at 75 mg/kg. PCNA was increased to a similar extent in both rats and mice, while apoptosis was decreased at both doses of CI-924 after 3 days in female rats, 7 days in male rats, and was largely unchanged in mice. It was concluded that the sequence of peroxisome proliferation was generally similar in rats and mice. Early changes in cell proliferation and programmed cell death were not directly correlated with subsequent CI-924-induced hepatotumorigenicity.

Animals↗
PubMed1981

Microsomal enzyme induction and gingival enlargement in subjects taking phenytoin.

Subjects taking the anticonvulsant phenytoin were examined for gingival enlargement and skin-fold thickness. Induced synthesis of their hepatic microsomal enzymes was estimated by measuring urinary D-glucaric acid. Gingival enlargement was positively correlated (p less than 0.05) with urinary D-glucaric acid. Although skin-fold thickness was not correlated with either urinary D-glucaric acid or gingival enlargement, mean gingival enlargement was greater in some subjects who did have an increased skin thickness than in those with normal skin thickness. The results suggest that induction of microsomal enzyme synthesis, as estimated by urinary D-glucaric acid, is related to taking phenytoin, as is gingival enlargement, and that there are other factors that affect both phenomena.

Adolescent↗
PubMed1984

Correlation between mixed-function oxidase enzyme induction and aflatoxin B1-induced unscheduled DNA synthesis in the chick embryo, in vivo.

The unscheduled DNA synthesis (UDS) technique has been adapted for use in the chick embryo, in vivo, to determine the relationship between induction of the mixed-function oxidase (MFO) enzyme system and genetic damage from an indirect-acting mutagen-carcinogen. Embryos were injected at 6 days of incubation (DI) with either phenobarbital (PB), a specific inducer of P-450-associated enzyme activities, or 3,4,3',4'-tetrachlorobiphenyl (TCB), a specific inducer of P1-450-associated enzyme activities. Aflatoxin B1 (AFB1) was injected 24 hr later (7 DI), followed by a 5-hr continuous 3H-thymidine exposure. The livers were removed, prepared for autoradiography, and hepatocytes were scored for an increase in grains/nucleus, indicative of UDS. Aflatoxin B1 caused a dose-related increase in UDS in all control and induction groups. Phenobarbital-induced embryos had an increased UDS response while TCB-induced embryos had a decreased UDS response, relative to noninduced embryos, for each dosage of AFB1. This suggests that the genotoxicity of an indirect-acting mutagen-carcinogen can be either increased or decreased, in vivo, depending on the inducer used. The chick embryo provides an excellent system for studying the effect of MFO induction on the genotoxicity of promutagen-carcinogens in a developing system.

Aflatoxin B1↗
PubMed1984

Intracellular localization of 2',3'-cyclic nucleotide 3'-phosphohydrolase in rat oligodendrocytes and C6 glioma cells, and effect of cell maturation and enzyme induction on localization.

We investigated whether the membrane-associated myelin enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP; EC 3.1.4.37), is localized primarily inside the cell or exposed on the cell surface of rat oligodendrocytes and rat C6 glioma cells. Determinations were made by enzyme assays of intact, viable cells vs cells broken by freezing and thawing. Assay of both oligodendrocytes and C6 cells showed that the great majority of the CNP activity was localized inside the cells. Oligodendrocytes were also tested by immunofluorescence staining of unfixed, living cells whose membranes had been made permeable to antibody by fixation. Fixed oligodendrocytes showed intense fluorescence when incubated with rabbit anti-CNP antiserum and fluorescein-conjugated second antibody whereas unfixed cells were not stained. We then tested the possible influence on CNP localization of 3 conditions known to increase CNP specific activity: maturation of oligodendrocytes in vitro during a period when CNP specific activity increases 8-fold or more; growth of C6 cultures to high cell density; and induction of CNP activity in oligodendrocytes and C6 cells by dibutyryl cyclic AMP. Under all conditions, most CNP activity was intracellular. These results show that both the catalytic and major antigenic sites of CNP are localized primarily inside the cell, and suggest an intracellular role for CNP in oligodendrocytes. The results with C6 cells also show that these cells resemble oligodendrocytes with respect to CNP localization.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗