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  • Title: Kinetics of liver microsomal cholecalciferol 25-hydroxylase in vitamin D-depleted and -repleated rats.
    Author: Delvin EE, Arabian A, Glorieux FH.
    Journal: Biochem J; 1978 Jun 15; 172(3):417-22. PubMed ID: 28728.
    Abstract:
    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.
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