11] Promotion of cyst(e)ine uptake

Abstract

This chapter focuses on the promotion of cyst(e)ine uptake. Besides its involvement in protein synthesis, the amino acid cysteine has a central function in the cellular metabolism of glutathione. The tripeptide glutathione, which can be defined as the intracellular “package form” of cysteine, is limited in regard to its biosynthesis by the availability of cysteine. Therefore, under conditions where the supply of cellular cysteine is not sufficient, a promotion of cysteine uptake by other chemical compounds would be expected to increase glutathione levels. In most eukaryotic cell types cysteine has to be taken up from the extracellular medium, but some cells (e.g., hepatocytes) are able to synthesize cysteine from methionine via the cystathionine pathway. For promotion studies of cysteine uptake different approaches can be taken. Exposure of CHO cells to thiols in vitro leads to enhanced intracellular glutathione levels via an increased uptake of cyst(e)ine. The use of such model systems where effects on intracellular glutathione play a major role may lead to a better understanding of the fundamental processes which are influenced by the availability of cyst(e)ine and intracellular thiol metabolism.