Studies of the chick renal mitochondrial 25-hydroxyvitamin D-3 24-hydroxylase.
The vitamin D metabolite, 24,25-dihydroxyvitamin D-3, is made from 25-hydroxyvitamin D-3 by an enzyme (25-hydroxyvitamin D-3 24-hydroxylase) located in the renal mitochondria of vitamin D and calcium-replete chicks. The apparent Km for 25-hydroxyvitamin D-3 for this reaction was found to be 3 x 10(-7) M, although simple Michaelis-Menten kinetics were not observed at the higher substrate concentrations. Enzymatic activity was reduced by the mitochondrial metabolic inhibitors, antimycin A and dinitrophenol, as well as the inhibitors of mixed function oxidases, 2,4-dichloro-6-phenylphenoxyethylamine, 2-diethylaminoethyl-2,2-diphenylvalerate and metyrapone. Increasing the calcium concentration from 0 to 1 x 10(-5) M or the potassium concentration from 0 to 50 mM stimulated enzymatic activity 4- to 8-fold. Increasing the phosphate or acetate concentration from 0 to 50 mM stimulated enzymatic activity 6-fold. Raising the CO2/HCO3(-) content from 0/0 to 10%/10 mM stimulated enzymatic activity 5-fold. The effects of the cations were additive to those of the anions except in the presence of 50 mM phosphate or acetate. The effect of ions on 24,25-hydroxyvitamin D-3 production by renal mitochondria from vitamin D-replete chicks resembles the effect of these ions on production of 1,25-dihydroxyvitamin D-3 by renal mitochondria from vitamin D-deficient chicks, suggesting that the same mechanisms may be utilized.
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002645:Chickens; D003577:Cytochrome P-450 Enzyme System; D005021:Ethylamines / Q000494:pharmacology; D006887:Hydroxycholecalciferols / Q000378:metabolism; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology; D010710:Phosphates / Q000494:pharmacology; D011078:Polychlorinated Biphenyls / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013250:Steroid Hydroxylases / Q000378:metabolism*; D065668:Vitamin D3 24-Hydroxylase
D000085:Acetates; D005021:Ethylamines; D006887:Hydroxycholecalciferols; D010710:Phosphates; C000939:2,4-dichloro-6-phenylphenoxyethylamine; C013721:1,24,25-trihydroxyvitamin D3; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D011188:Potassium; D002118:Calcium