Purification of cytochrome P-450 catalyzing 25-hydroxylation of vitamin D3 from rat liver microsomes

Cytochrome P-450 catalyzing 25-hydroxylation of cholecalciferol (cytochrome P-450 cc25 ) was purified from rat liver microsomes based on its catalytic activity at each purification step. The specific cytochrome P-450 content of the final preparation was 15.1 nmol/mg of protein. Reconstituted activity of 25-hydroxylation of cholecalciferol with the purified enzyme was 2.3 nmol/min/mg of protein, which was 4,300 times as high as that in microsomes. The minimum molecular weight of the enzyme was 50,000 based on SDS-polyacrylamide gel electrophoretogram. Amino terminal sequence of the P-450 cc25 was H2N-Met-Asp-Pro-Val-Leu-Val-. Immunochemical study showed that the purified P-450 cc25 was homogeneous and the cytochrome was immunochemically different from either cytochrome P-450(PB-1) or cytochrome P-448(MC-1).