3 -Hydroxy steroid dehydrogenase activity in the mitochondria of rat adrenal homogenates.
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ABSTRACT:
SUBMITTER: Basch RS
PROVIDER: S-EPMC1178260 | biostudies-other | 1971 Dec
REPOSITORIES: biostudies-other
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Project description:Steroidogenesis by adrenal mitochondria from endogenous precursors is stimulated by corticotropin (ACTH) and is sensitive to the protein-synthesis inhibitor cycloheximide. In the present investigation the effect of cycloheximide treatment on the metabolism of a number of analogues of the normal steroidogenic substrate, i.e. cholesterol, by rat adrenal mitochondria was studied. It was observed that the metabolism of analogues such as desmosterol, 26-norcholest-5-en-3beta-ol and 5-cholen-3beta-ol (that is with non-polar alkyl side chains like cholesterol), was sensitive to cycloheximide treatment. By contrast, the metabolism of those analogues with polar groupings on the side chain, i.e., 20alpha-, 24-, 25- and 26-hydroxycholesterols was insensitive to pretreatment with cycloheximide. The binding of added sterol to the cytochrome P-450 component of the mitochondrial sterol desmolase was studied. Similar studies on the equilibration time on addition of exogenous sterols to achieve maximum rates of pregnenolone production were also made. Both studies show that cholesterol, a non-polar sterol, penetrated slowly through the mitochondrial milieu to reach the cytochrome P-450 reaction centre whereas 24- and 26-hydroxycholesterols rapidly attained the enzymic environment. The cycloheximide-sensitive process in sterol metabolism appeared related to the transfer of non-polar sterols such as cholesterol within the mitochondria to a region in close proximity to the enzyme. The importance, and possible mechanism of action, of the cycloheximide-sensitive factor in the control of adrenal steroidogenesis is discussed.
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Project description:Glucose 6-phosphate dehydrogenase activity in rat liver mitochondria can be released by detergent. The released activity is separated by chromatography into two peaks. One peak has the kinetic behaviour and mobility similar to the soluble sex-linked enzyme, whereas the other peak is similar to the microsomal hexose 6-phosphate dehydrogenase. There is no evidence for the existence of a new glucose 6-phosphate dehydrogenase activity in rat liver mitochondria.
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Project description:Background: Studies suggest that indomethacin (Indo) exhibits detrimental changes in the small intestine (microvascular disorder, villus shortening, and epithelial disruption), mainly due to mitochondrial uncoupling. The effects of Indo on colon and liver tissue are unclear. The aim of this study was to determine the effects of Indo on mitochondrial respiration in colonic and hepatic tissue. Methods: Mitochondrial oxygen consumption was assessed in colon and liver homogenates from healthy rats. Homogenates were incubated without drug (control) or Indo (colon: 0.36, 1, 30, 179, 300, 1,000, 3,000 μM; liver: 0.36, 1, 3, 10, 30, 100, 179 μM; n = 6). State 2 (substrate-dependent) and state 3 (ADP-dependent respiration) were evaluated with respirometry. The respiratory control index (RCI) was derived and the ADP/O ratio was calculated. Statistics: Data presented as % of control, min/median/max, Kruskal-Wallis+Dunn's correction, * p < 0.05 vs. control. Results: Indo had no effect on RCI of colonic mitochondria. ADP/O ratio increased in complex I at concentrations of 1,000 and 3,000 μM (Indo 1,000 μM: 113.9/158.9/166.9%*; Indo 3,000 μM: 151.5/183.0/361.5%*) and in complex II at concentrations of 179 and 3,000 μM vs. control (179 μM: 111.3/73.1/74.9%*; 3,000 μM: 132.4/175.0/339.4%*). In hepatic mitochondria RCI decreased at 179 μM for both complexes vs. control (complex I: 25.6/40.7/62.9%*, complex II: 57.0/73.1/74.9%*). The ADP/O ratio was only altered in complex I at a concentration of 179 μM Indo vs. control (Indo 179 μM: 589.9/993.7/1195.0 %*). Conclusion: Indo affected parameters of mitochondrial function in an organ-specific and concentration-dependent manner. In colonic tissue, RCI remained unaltered whereas the ADP/O ratio increased. Indo at the highest concentration decreased the RCI for both complexes in hepatic mitochondria. The large increase in ADP/O ratio in complex I at the highest concentration likely reflects terminal uncoupling.
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