JBC, Vol. 250, Issue 11, 4067-4072, Jun, 1975
Effects of pentanoic acid and 4-pentenoic acid on the intracellular fluxes of acetyl coenzyme A in Tetrahymena
G. J. Raugi, T. C. Liang and J. J. Blum
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.
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