Abstract
Kinetics of vitamin D-repleted guinea pig kidney mitochondrial 25-hydroxycholecalciferol-1α-hydroxylase were studied. Omission of malate, source of mitochondrial reducing equivalents, abolished the 1α-hydroxylase activity as well as the degradation of 1α,25-dihydroxycholecalciferol [1,25(OH) 2D 3], indicating that both functions shared elements of a common pathway. Preincubation of the mitochondrial preparation in presence of 10 n m 1,25(OH) 2D 3 for 15 min protected the labeled 1,25(OH) 2D 3 from degradation. Under these conditions an apparent K m of 605 n m and a V max of 40 pmol/ 30 min/mg mitochondrial protein were observed. These data show that this particular mammalian model may be used to study the modulation of mammalian 1α-hydroxylase activity.
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