Effects of cholecalciferol (vitamin D3)-binding proteins and anti-cytochrome b5 immunoglobulin on cholecalciferol 25-hydroxylase activities of rabbit liver microsomes and mitochondria

Abstract

The effects of cholecalciferol (vitamin D3)-binding proteins and anti-cytochrome b5 immunoglobulin were studied on vitamin D3 25-hydroxylase activities of microsomes and mitochondria under various experimental conditions. The vitamin D3-binding protein in serum as well as in the liver postmicrosomal supernatant (cellular vitamin D3-binding protein), but not serum albumin and ovalbumin, stimulated vitamin D3 25-hydroxylase activities of microsomes and mitochondria. The optimum pH range was from 7.3 to 8.0. Anti-cytochrome b5 immunoglobulin did not affect microsomal vitamin D3 25-hydroxylase activity.