PURIFICATION FROM PIG-KIDNEY OF A MICROSOMAL CYTOCHROME-P-450 CATALYZING 1-ALPHA-HYDROXYLATION OF 25-HYDROXYVITAMIN D-3

A cytochrome P-450 catalyzing 1 alpha-hydroxylation of 25-hydroxyvitamin D-3 was purified from pig kidney microsomes. The enzyme preparation showed one protein band on gel electrophoresis with apparent M(r) of 52,500 and a specific cytochrome P-450 content of 10.7 nmol/mg of protein, The 25-hydroxyvitamin D-3 1 alpha-hydroxylase copurified with the vitamin D-3 25-hydroxylase during purification. A cytochrome P-450 catalyzing 1 alpha-hydroxylation was purified also from liver microsomes, The apparently homogeneous enzyme showed the same catalytic properties and apparent M(r) as the kidney enzyme, The results of the present communication demonstrate the presence in kidney of a previously unknown microsomal 1 alpha-hydroxylase in addition to the assumed specific mitochondrial 1 alpha-hydroxylase. The possibility that microsomal 1 alpha-hydroxylation in pig kidney and liver is catalyzed by the previously described porcine microsomal vitamin D 25-hydroxylase(s) is discussed.