Subcellular localization of vitamin D3 25-hydroxylase in human liver.
Vitamin D3 25-hydroxylase activity was measured in subcellular and submitochondrial fractions of human liver. Quantitation of 25-hydroxyvitamin D3 was based on high performance liquid chromatography. Vitamin D3 25-hydroxylase activity was detected in the mitochondrial fraction only. The mitochondrial 25-hydroxylase activity was linear with time up to 60 min and with mitochondrial protein up to 1 mg/ml. An apparent Km value of about 10(-5) M was found. Substrate satuation level was not reached. In the presence of 2.4 X 10(-4) M vitamin D3, the rate of 25-hydroxyvitamin D3 formation was 0.19 nmol X mg of protein-1 X h-1 After fractionation of the mitochondria, 86% of the 25-hydroxylase activity was recovered in the mitoplast fraction. The outer membrane fraction was devoid of activity. It is concluded that human liver contains only one detectable vitamin D3 25-hydroxylase enzyme localized to the mitochondrial inner membrane.
D002458:Cell Fractionation; D002467:Cell Nucleus / Q000201:enzymology; D053493:Cholestanetriol 26-Monooxygenase; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D007425:Intracellular Membranes / Q000201:enzymology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D013250:Steroid Hydroxylases / Q000302:isolation & purification* / Q000378:metabolism
D013250:Steroid Hydroxylases; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase