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The cysteine transport system of Saccharomyces cerevisiae
Author(s) -
Ono BunIchiro,
Naito Kazuhide
Publication year - 1991
Publication title -
yeast
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.923
H-Index - 102
eISSN - 1097-0061
pISSN - 0749-503X
DOI - 10.1002/yea.320070810
Subject(s) - cysteine , cysteic acid , methionine , biochemistry , cysteamine , saccharomyces cerevisiae , cysteine metabolism , glutathione , amino acid , biology , homocysteine , yeast , cystine , enzyme
Although Saccharomyces cerevisiae strains had different cysteine uptake activities, they revealed monophasic uptake kinetics and had the same K T (83·3 μ M ). The optimal pH of cysteine uptake was between 4·5 and 5·0, but the activity was quickly lost if cells were kept in buffer. When the activity was measured in the growth medium, it increased in the presence of EDTA and greatly decreased in the presence of mercuric chloride. Thioglycol as well as metabolic inhibitors such as dinitropherol and azide were inhibitory. Homocysteine and methionine were competitive and non‐competitive inhibitors, respectively. Cysteamine and cysteic acid were not inhibitory. From these observations, we conclude that the system mediating uptake of cysteine is specific (we thus name it the cysteine transport system) and that the cysteine transport system recognizes not only the SH‐group but also amino‐ and carboxyl‐groups. In wild‐type strains the cysteine transport system was derepressed only when the cells were incubated without any sulfur source. On the other hand, in cysteine‐dependent mutants, cysteine uptake activity increased with increase of exogenous supply of cysteine, glutathione or methionine. From this result, we suspect that the cellular cysteine level is the limiting factor for biosynthesis of the cysteine transport system in cysteine‐dependent strains.