Effect of [formula omitted] on leucine transport in chang liver cells. I. Stimulatory effect on Na +-independent transport at low concentrations of leucine

Abstract

Pretreatment of Chang liver cells with N- ethylmaleimide (0.5 or 1 mM) stimulated Na +-independent uptake of leucine at low concentrations (⩽1 mM). The stimulatory effect of N- ethylmaleimide on the uptake of leucine measured in Na +-replete medium was completely blocked by the addition of b-2- aminobicyclo[2,2,1] heptane-2- carboxylate (5 mM), which shows that the L system participates in the stimulation. The Na +-dependent uptake of glycine was depressed by N- ethylmaleimide pretreatment. The stimulation of the Na +-independent component of leucine uptake continued for at least 30 min after N- ethylmaleimide treatment, while the inhibition of glycine uptake was progressive with time and the Na +-dependent uptake of leucine became depressed later, after the treatment. It has been demonstrated that treatment of cells with N- ethylmaleimide is capable of increasing the Na +-independent influx of leucine and at the same time slightly decreasing the efflux of it. These results suggest that N- ethylmaleimide attacks the Na +-independent system of amino acid transport at the reactive SH groups(s) of relevant protein(s) in favor of specific activation of that system in this cell.