Effects of pentanoic acid and 4-pentenoic acid on the intracellular fluxes of acetyl coenzyme A in Tetrahymena.

Cultures of Tetrahymena pyriformis were incubated for 1 hour with a mixture of acetate, pyruvate, and pentanoate with only one substrate labeled at a time and with the position of the label chosen so that [1-14-C]acetyl coenzyme A was an early product of the metabolism of each substrate. The appearance of label in CO2, lipids, glycogen, glutamate, and alanine were measured and results interpreted in terms of a previously developed three-compartment model of metabolism, which was found to quantitatively describe the data even when two of the flux rates (the flux of acetyl-CoA from the peroxisomal to the outer mitochondrial compartment and from the outer mitrochondrial to the inner mitochondrial compartment) were set equal to zero. This reduction in the number of independent parameters leads to the model being overdetermined and to a probably unique fit of the three-compartment model tof the present data and to previous data when octanoate was the fatty acid substrate. Pentanoate was metabolized to a greater extent than octanoate and did not inhibit growth. Pentanoate inhibited acetate utilization in both the inner mitochondrial and peroxisomal compartments as indicated by a reduction in the incorporation of label from [1-14-C]acetate into lipids and into CO2, but there was no difference in oxidation of [2-14-C]pyruvate when pentanoate was the fatty acid substrate as compared to octanoate. Glyconeogenesis was inhibited when pentanoate was substituted for octanoate. Similar experiments were performed on cells treated with 4-pentenoic acid. The effects of 4-pentenoic acid were essentially the same whether octanoate or pentanoate was the fatty acid substrate, i.e. inhibition of glyconeogenesis from all labeled substrates and inhibition of [2-14-C]pyruvate oxidation. The results indicate that the effects of pentanoate are largely confined to the peroxisomal and the inner mitochondrial compartments whereas the effects of 4-pentenoic acid are confined to the peroxisomal and outer mitochondrial compartments.