HETEROGENEITY IN RABBIT LIVER CYTOCHROME-P-450 LM2 OBSERVED BY CATION-EXCHANGE HPLC - PARTIAL BIOCHEMICAL-CHARACTERIZATION OF THE 2 MAJOR LM2 SUBFRACTIONS

Cytochrome P450 LM2 (CYPIIB4) from phenobarbital-induced rabbit liver microsomes, purified to only one band in SDS-PAGE, was further resolve d in five peaks by cation exchange HPLC. The two major peaks were part ially characterized. Both of them have the amino terminal sequence Met -Glu and the same Cys content. They exhibited the same spectral absorp tion maximum and similar binding constants for 1-benzylimidazole and i midazole. However, binding of benzphetamine was different. One subfrac tion presented a Michaelis-Menten type binding curve, but the other pr esents a non-typical one with an additional high affinity binding site . These subfractions of cytochrome P450 LM2 slightly differed in their catalytic activities with benzyloxy- and pentoxyresorufin substrates. On the contrary, no heterogeneity was observed for P450 LM4.