Utilization of methylmalonate for the synthesis of branched-chain fatty acids by preparations of chicken liver and sheep adipose tissue.

1. The utilization of methyl[2-14C]malonyl-CoA for fatty acid synthesis was investigated using synthetase preparations from chicken liver and sheep adipose tissue. 2. The rate of fatty acid synthesis from acetyl-CoA and malonyl-CoA was greatly diminished in the presence of methylmalonyl-CoA. 3. In the absence of malonyl-CoA, methylmalonyl-CoA was utilized for fatty acid synthesis only very slowly by the synthetase from sheep adipose tissue and not at all by that from chicken liver. 4. Despite the inhibitory effect of methylmalonyl-CoA on fatty acid synthesis from malonyl-CoA, it was utilized by the synthetase preparations from both species to produce a complex mixture of methyl-branched fatty acids.