Abstract
The possible involvement of cytochrome b5 in NADPH-mediated cytochrome P-450 reactions in liver microsomes was first suggested by Estabrook and co-workers (1,2). Two years ago we presented immunochemical evidence that the synergistic effect of NADH on NADPH-mediated ethylmorphine metabolism by rat liver microsomes is indeed mediated through cytochrome b5 by showing that an antibody against rat liver cytochrome b5 blocks the increase in NADH-oxi-dation and ethylmorphine N-demethylation in the presence of NADPH, ethylmorphine and liver microsomes (3). We recently presented evidence that a sheep antibody against cytochrome b5 (4,5) also inhibits the omega hydroxylation of lauric acid by rat liver and kidney cortex microsomes in the presence of either NADH or NADPH (Table I). In order to differentiate the inhibitory effect of sheep antibody against cytochrome b5 on the omega hydroxylation of lauric acid from some nonspecific inhibitor present in the antibody preparation, we preincubated the antibody with varying amounts of purified, trypsin-solubilized cytochrome b5 from rat liver and then examined the reversibility of the inhibitory effect.
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