Kinetics of liver microsomal cholecalciferol 25-hydroxylase in vitamin D-depleted and -repleated rats.
Kinetics of vitamin D-depleted and -repleted rat liver microsomal cholecalciferol 25-hydroxylase were studied. Anaerobiosis, CO, omission of a NADPH-generating system and addition of detergents all decreased the activities, showing that the hydroxylase behaves like a cytochrome P-450-dependent enzyme. An apparent Km of 0.18 micrometer and Vmax. of 32pmol/min per g of tissue were found for vitamin D-deficient animals. Although both apparent Km and Vmax. were significantly altered in vitamin D-repleted animals no inhibition of the enzyme was elicited. These latter results show that at normal vitamin D intake, rat liver cholecalciferol 25-hydroxylase is not feedback-inhibited.
D000693:Anaerobiosis; D000818:Animals; D002248:Carbon Monoxide / Q000494:pharmacology; D002762:Cholecalciferol; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009249:NADP / Q000378:metabolism; D051381:Rats; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013501:Surface-Active Agents / Q000494:pharmacology; D014808:Vitamin D Deficiency / Q000201:enzymology*
D013501:Surface-Active Agents; D002762:Cholecalciferol; D009249:NADP; D002248:Carbon Monoxide; D013250:Steroid Hydroxylases