Side-chain oxidation of vitamin D3 in mouse kidney mitochondria: effect of the Hyp mutation and 1,25-dihydroxyvitamin D3 treatment.
Side-chain oxidation of vitamin D is an important degradative pathway. In the present study we compared the enzymes involved in side-chain oxidation in normal and Hyp mouse kidney. Homogenates of normal mouse kidney catalyze the conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3, 24-oxo-25-hydroxyvitamin D3 and 24-oxo-23,25-dihydroxyvitamin D3. After subcellular fractionation, total side-chain oxidative activity, estimated by the sum of the three products synthesized per milligram protein under initial rate conditions, coincided with the mitochondrial enzyme marker succinate-cytochrome-c reductase. Treatment of normal mice with 1,25-dihydroxyvitamin D3 (1.5 ng/g) resulted in an eightfold increase in mitochondrial enzyme activity, with no change in apparent Km but a significant rise in Vmax. With 24,25-dihydroxyvitamin D3 as the substrate, normal renal mitochondria produced 24-oxo-25-hydroxyvitamin D3 and 24-oxo-23,25-dihydroxyvitamin D3, and the synthesis of these metabolites could be increased sixfold by pretreatment with 1,25-dihydroxyvitamin D3. In the Hyp mouse, the side-chain oxidation pathway showed similar subcellular distribution of enzyme activity. However, product formation from 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 was twofold greater in mutant than in normal mitochondria. Furthermore, 1,25-dihydroxyvitamin D3 pretreatment of Hyp mice resulted in a 3.4-fold increase over basal metabolism of both 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3. These results demonstrate that (i) kidneys from normal and Hyp mice possess basal and 1,25-dihydroxyvitamin D3 inducible enzyme system(s) in the mitochondrial fraction, which catalyze the side-chain oxidation of 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3, and (ii) the Hyp mutation appears to perturb the renal metabolism of both substrates only in the basal state.
Jones
G
G
Department of Medicine, Queen's University, Kingston, Ont., Canada.
Yip
A
A
Tenenhause
H S
HS
D000818:Animals; D002117:Calcitriol / Q000008:administration & dosage*; D002762:Cholecalciferol / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000201:enzymology*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D002762:Cholecalciferol; D010088:Oxidoreductases; D002117:Calcitriol