Possible involvement of NADPH-cytochrome P450 reductase and cytochrome b5 on beta-ketostearoyl-CoA reduction in microsomal fatty acid chain elongation supported by NADPH.

The chain elongation products from [2-14C]malonyl-CoA and palmitoytl-CoA by rat liver microsomes initiated by NADPH were found mainly to be 18:1 and 18:0. When anti-NADPH-cytochrome P450 reductase or anti-cytochrome b5 immunoglobulin G were included in this system, not only was the overall chain elongation significantly suppressed, but also a new radioactive product, which was identified as 2-heptadecanone derived from an intermediate beta-ketostearate, is accumulated depending upon the amounts of IgG added. These results suggest that NADPH-cytochrome P450 reductase and cytochrome b5 participate in the conversion from beta-ketostearoyl-CoA to beta-hydroxystearoyl-CoA, which is the first reductive step of the microsomal chain elongating system.