Relative incorporation of the various propionate carbons into fatty acids by lactating rat mammary gland

Abstract

1. 1. Propionate labeled with 14C in each of its carbons was incubated with slices prepared from lactating rat mammary glands. In the absence of added glucose, 14C of [2- 14C]propionate was more rapidly incorporated into fatty acids than was 14C of either [1- 14C]propionate or [3- 14C]propionate. 2. 2. The addition of glucose to the medium increased fatty acid synthesis from all three carbons of propionate. The 14C of [2- 14C]propionate and [3- 14C]propionate was incorporated at identical rates and exceeded that from [1- 14C]propionate. 3. 3. Unlabeled acetate, at low concentrations in the presence of glucose, depressed conversion of 14C of [1- 14C]propionate into fatty acids. At higher acetate concentrations the conversion from all propionate carbons was depressed. 4. 4. The [ 14C]fatty acids synthesized from [1- 14C]-,[2- 14C]- and [3- 14C]propionate were subjected to gas-chromatographic analysis, and the presence of both-even-chain [ 14C]fatty acids and odd-chain [ 14C]fatty acids was demonstrated. 5. 5. The results suggest that there are at least three pathways for conversion of propionate carbon to fatty acids by lactating rat mammary gland. Direct condensation with malonyl-CoA to form odd-chain fatty acids is by far the most predominant pathway. Glucose stimulated incorporation of propionate carbon into fatty acids by all three pathways equally.