title: Hepatic 7alpha-hydroxylation of cholesterol in ascorbate-deficient and ascorbate-supplemented guinea pigs.
abstract: Cholesterol 7alpha-hydroxylase activity was assayed in liver microsomes from guinea pigs supplemented with ascorbate and from guinea pigs in a state of ascorbate deficiency. A mass fragmentographic method was used by which the 7alpha-hydroxylation of endogenous cholesterol could be measured. The 7alpha-hydroxylation was markedly reduced in the ascorbate-deficient animals as compared to animals treated with ascorbate. Addition of ascorbate to the incubations did not increase this activity. 11- and 12-Hydroxylation of laurate as well as 25- and 26-hydroxylation of 5beta-cholestane-3alpha, 7alpha-diol were not significantly affected by the ascorbate status of animals. In the presence of excess NADPH-cytochrome P-450 reductase and a phospholipid, partially purified cytochrome P-450 from the microsomal fraction of liver of an ascorbate-deficient guinea pig had a much lower capacity to 7alpha-hydroxylate [4-14C]cholesterol than a corresponding system containing cytochrome P-450 from liver of an ascorbate-supplemented guinea pig. It is suggested that ascorbate affects the synthesis or breakdown of the 7alpha-hydroxylating system, in particular the cytochrome P-450 component.
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology*; D001206:Ascorbic Acid Deficiency / Q000201:enzymology*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D002790:Cholesterol 7-alpha-Hydroxylase; D001205:Ascorbic Acid