The synthesis and some of the physical and
biological characteristics of a new inhibitor of
lactate transport are described. The inhibitor is isobutylcarbonyl lactayl
anhydride (
iBCLA). It is formed by the condensation of
lactic acid and isobutylchloroformate. It inhibits
lactate transport 50% at 0.5 microgram/mg of
protein in both
Ehrlich ascites tumor cells and human erythrocytes. In contrast, 15 microgram of
iBCLA/mg of
protein is required for 50% inhibition of
phosphate transport in erythrocytes, and
phosphate transport in
Ehrlich ascites tumor cells is unaffected at levels as high as 50 microgram of
iBCLA/mg of
protein. A time-dependent and concentration-dependent reversal of
lactate transport inhibition took place on exposure of
iBCLA-treated Ehrlich
ascites cells to
hydroxylamine or
dithiothreitol. These data, along with the observed sensitivity of the
lactate transporter to
sulfhydryl reagents [Spencer, T. L., & Lehninger, A. L. (1976) Biochem. J. 154, 405-414], suggest that
iBCLA acylates an essential sulfhydryl group on the transporter. When glycolyzing
Ehrlich ascites tumor cells were treated with concentrations of
iBCLA sufficient for complete inhibition of
lactate transport, intracellular
lactate levels increased, intracellular pH and extra-cellular
lactate levels decreased, and overall
lactate production was inhibited.