Current microsomal model has P450 (CYP) and NADPH-P450 reductase moving about and colliding through the phospholipid membrane with the tails of each protein as membrane anchors, and using the recognition sites in protein–protein interactions to make contacts and facilitate electron transfer. However, there is still an element of mystery about the stoichiometry in the endoplasmic reticulum, which is usually one molecule of NADPH-P450 reductase provides electrons to app. 20 molecules of total P450 (we don't specify here that in some cases, cytochrome b5 is also involved). Exactly how does this system work in this apparent deficiency of reductase? Moreover, the most sophisticated (at the time) methods using purified P450 and its reductase did not answer the above question. Thus although both cholate dialysis and gel filtration methods improved protein incorporation into lyposome when compared to preincubation of proteins with preformed liposomes, the reductase incorporation was complete at a 0.2:1 reductase to P450 ratio. However, to achieve some rather insignificant level of enzyme activity of the system (say, CYP2B4 catalyzing benzphetamine N-demethylation), the above level might be reached only at a 5:1 reductase to P450 ratio.
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