Biochemical properties of cytochrome b5-dependent microsomal fatty acid elongation and identification of products.

Abstract

In this paper, a correlation between the rates of ba reoxidation in the presence of malonyl-CoA and malonyl-CoA incorporation measured under various conditions was demonstrated, thus providing further evidence in support of our hypothesis.The additional data in this paper detail the biochemical characteristics of the microsomal fatty acid elongation reaction.The rates of ba reoxidation and malonyl-CoA incorporation were linear with protein concentration up to 2 mg/ml and were optimal between pH 7.2 and 7.4.The rates were linear with malonyl-CoA concentration up to 3 PM and were maximal at 20 CM with a K,,, of 8 PM.The bg reoxidation rate was always 10 to 15% faster than the incorporation rate.The products formed during fatty acid elongation were 18:O (15%), 18:1(65%), and 20:1(20%) using either NADH or NADPH as the reducing agent.The rate of incorporation was 30% faster with NADPH than with NADH, although the extent of incorporation was nearly identical.The apparent K,,, was 7 PM for NADH and 8