TABLE 2

Kinetic parameters for hydroxylation of 22(OH)D₃ and 20(OH)D₃ by P450scc

Kinetic constants were determined for substrates incorporated into phospholipid vesicles prepared from dioleoyl phosphatidylcholine and cardiolipin. Substrate concentrations are expressed as moles of substrate per mole of phospholipid (PL). Values for K_m and k_cat are means ± S.E. from the hyperbolic curve fitted to the data by least-squares nonlinear regression using KaleidaGraph 4.1.

Substrate	Hydroxylation Site	K_m	k_cat
		mol/mol PL	min⁻¹
22(OH)D₃	C20	0.15 ± 0.08	2.09 ± 0.90
20(OH)D₃	C17	0.27 ± 0.04	0.47 ± 0.04
20(OH)D₃	C22	0.16 ± 0.01	0.43 ± 0.01
20(OH)D₃	C23	0.25 ± 0.01	1.55 ± 0.06