when the amount of [ 3h ] -25-hydroxyvitamin d3 formed was expressed in relation to the amount of enzyme present in the reaction medium , a constant c-25 hydroxylation capacity in all age groups was observed suggesting that the cytochrome p-450 isoenzyme responsible for the c-25 hydroxylation of vitamin d3 may be constitutionally determined and that its appearance originates during fetal life .
C0014442
enzyme
C0022173
isoenzyme