ArticleSaarem K, Pedersen JI, Tollersrud S.
Comp Biochem Physiol B. 1978;61(4):485-90.
1. Mitochondria isolated from the kidneys of rachitic pigs have been shown to contain an active 25-hydroxyvitamin D3-1 alpha-hydroxylase. From these mitochondria a cytochrome P-450 has been solubilized with a specific content of 0.02-0.04 nmol/mg protein. 2. In the presence of a bovine adrenal NADPH-ferredoxin reductase, bovine adrenal ferredoxin and NADPH, the cytochrome P-450 supported the formation of 1,25-dihydroxyvitamin D3 from 25-hydroxyvitamin D3. 3. The hydroxylation reaction was linear with time up to 40 min, and with the amount of enzyme up to 0.03 nmol cytochrome P-450. The pH optimum for the reaction was 7.4, and the apparent Km was 3 x 10(-10) mol/mg protein. 4. The results show that 25-hydroxyvitamin D3 is metabolized in mammals by the same enzyme system as has been demonstrated in birds.