Metabolism of branched-chain fatty acids in Tetrahymena pyriformis W

Abstract

Cultures of Tetrahymena pyriformis W were supplemented with the branched short-chain acids, isobutyrate and α-methyl- n-butyrate. Growth inhibition occurred which was directly related to the concentration of the supplement. Growth of the cells with isobutyrate resulted in an enhancement in the levels of even iso and normal fatty acids, a decrease in odd iso fatty acids, and an elevation in fatty acids less than 18 carbons in chain length. The data indicate a reduction in overall cellular branched-chain synthesis. Polyunsaturated, long-chain iso acids were not detected. Addition of α-methyl- n-butyrate led to minimal incorporation (2%) of saturated long-chain anteiso fatty acids and to a marked increase in odd normal acids at the expense of odd iso and even normal acids in the glycerophospholipids and in neutral lipids. An elevation of odd normal α-hydroxy acids in the sphingolipids was observed. The metabolism of α-methyl- n-butyrate to propionyl-CoA which serves as a primer for odd normal acids would account for the observed changes. Unsaturated anteiso components were not detected. Enhancement of the amount of anteiso acids occurred when the cells were grown at low temperature with α-methyl- n-butyrate. Long-chain anteiso acids (C 15, C 17 and C 19) were incorporated extensively into the glycerophospholipids at the expense of odd iso, odd normal and even normal acids. Anteiso unsaturates were not detected. Elongation of 15 : 0( ai) and 17 : 0(ai) occurred. Retroconversion of 17 : 0(af) and 19 : 0(ai) was observed. Growth with 17 : 0( ai) and 19 : 0( ai) but not 15 : 0( ai) led to the appearance of 19 : 0( ai, α-OH) in the sphingolipid fraction. The fact that addition of these long-chain anteiso saturates led to an enhanced incorporation into the glycerophospholipids compared to supplementation with α-methyl- n-butyrate indicates that a defect in the synthesis of long-chain acids occurs and that acyltransferase activity is not limiting in anteiso acid incorporation. A proposal is made to account for the low levels of unsaturated even iso acids and the lack of unsaturated anteiso acids based on Δ 9 desaturase specificity toward carbon chain length and the position of the methyl substituent in the fatty acid.