Open AccessEffects de la lysine sur la synthèse et l'activité de l'arginase et de l'ornithine transaminase chez Saccharomyces cerevisiae
Author(s) -
Bourgeois Claude M.,
Thouvenot Daniel R.
Publication year - 1970
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1970.tb00988.x
Subject(s) - arginase , derepression , ornithine , lysine , arginine , biochemistry , transaminase , enzyme , biology , chemistry , amino acid , psychological repression , gene expression , gene
Recently evidence has been presented of an inhibitory effect of l ‐lysine upon post‐exponential growth of Saccharomyces cerevisiae , which seems to be related to a very low arginine pool (ten to twenty times lower than usual). Explanation of this phenomenon has been sought in a study of the effects of l ‐lysine upon arginine catabolic enzymes. It has been shown that the presence of 5 mM l ‐lysine in a medium containing 10 mM ammonium sulfate results in an important increase of arginase and ornithine transaminase activities during exponential growth: arginase activity increases roughly from 6 to 40 milliunits; ornithine transaminase activity is four times higher than the usual maximum, even during exponential growth, but shows then no starvation derepression. The addition of l ‐lysine in the course of exponential growth results immediately in a derepression of both enzymes, which is then lengthened by the starvation derepression. Properties of both enzymes have been studied with crude extracts after Sephadex filtration. The K m of arginase towards arginine has been found to be equal to 5.1 mM; study of lysine effects at two concentrations of substrate (50 mM, 5 mM) has shown that l ‐lysine exerts a competitive inhibition with a K i equal to 1.9 mM. On the other hand l ‐lysine has no effect upon ornithine transaminase activity. Growth studies of an arginine‐auxotrophic mutant, with or without lysine, have shown that 1 mM l ‐lysine inhibits post‐exponential growth if arginine concentration is low, but does not inhibit it if arginine concentration is higher than 0.6 mM; this is in accordance with the explanation of growth inhibition by the effect upon arginine metabolism. Since an arginase‐deficient mutant remains as sensitive as the wild type to lysine effect upon growth, this effect is more likely to be attributed to negative influence on biosynthesis than to positive influence on catabolism.