La semi-aldehyde aspartique deshydrogenase chez Saccharomyces cerevisiae: proprietes et regulation

Abstract

The synthesis of threonine and methionine in X. cerevisiae proceeds as follows :aspartic acid + aspartyl-phosphate + aspartic-semi-aldehydeThe aspartic-semi-aldehyde dehydrogenase (ASA dehydrogenase) catalyzes the second reaction. It has been purified from an extract of baker's yeast and has been obtained with a specific activity 250 times higher than in crude extracts. Its main properties are : (a) The optimum pH is 8.5 in both directions; (b) Its activity is enhanced 4 or 5 times in both directions by addition of bicarbonate to the reaction mixture. Evidence is presented that the bicarbonate is necessary for the reaction to proceed; (c) Its molecular weight estimated by filtration on Sephadex G-200 is about 140,000; (d) No feed-back inhibition by threonine or methionine has been found. An inhibition by cysteine and homocysteine (Kt = 1 x M) was found in the reverse reaction.The synthesis of ASA dehydrogenase is regulated by threonine intracellular concentration ; (e) By heating at 60" a t different pH's it is shown that ASA dehydrogenase exists in two forms. Two mechanisms are proposed: a depolymerisation, or a release of proton. As in the case of the ~-glyceraldehyde-3-phosphate dehydrogenase, the reaction catalyzed by ASA dehydrogenase can be separated into two parts : the oxidation and the phosphorylation. This mechanism is under investigation. Abrbviations non usudles. Semi-aldbhyde aspartique,

An integrated study of threonine-pathway enzyme kinetics in Escherichia coli

“…This compound was characterized in HPLC by observing which peak was transformed into homoserine by HDH. ASA concentration was assessed by an enzymic assay using HDH and by measuring the NADPH consumption at 340 nm [25]. Like Szczesiul and Wampler [3], we observed no significant loss of substrate activity in 0.1 M HCl at k80 mC in 1 year.…”

“…These values have never been determined in E. coli, as far as we know, but can be compared with the corresponding values found in Saccharomyces cere isiae [25]. We obtained a lower value for K aspp (0.022p0.001 mM instead of 0.27 mM) and a similar value for K NADPH (0.029p0.002 mM instead of 0.03 mM).…”

Four major transcriptional responses in the methionine/threonine biosynthetic pathway of Saccharomyces cerevisiae

“…Nass and Hascnbank (1970); "'de Robichon-S7ulmajster 6'101. (1973): "Surdin (1967);PLor and Cossins (1972); T h o m a s 1…”

Aspartate‐β‐Semialdehyde Dehydrogenase from Escherichia coli

“…This enzyme had been purified from yeast [2,3] and from Escherichia coli [4j. In the present study an improvement of the purification of the E. coli enzyme is given, and the amino acid composition, chemical and physicochemical properties are described.…”

“…In order to investigate similarities and differences between phosphorylating aldehyde dehydrogenases, structural and mechanistic studies of the aspartate-8-semialdehyde dehydrogenase were undertaken. This enzyme had been purified from yeast [2,3] and from Escherichia coli [4j. In the present study an improvement of the purification of the E. coli enzyme is given, and the amino acid composition, chemical and physicochemical properties are described.…”