Year: 1972
Type: article
Abstract: Homoserine dehydrogenase is a key enzyme in the biosynthesis of methionine, threonine and isoleucine (Greenberg, 1969; Meister, 1965) from aspartate.So far there appear to be only two instances of homoserine dehydrogenase subject to complete re- pression by methionine, namely in Escherichia coli K12 (Patte et al., 1967, 1969) and in Salmonella typhimurium (Cafferata & Freundlich, 1969, 1970).However, these organisms possess two homoserine dehydrogenases and the methionine-repressible enzyme is a minor one.A strain of Serratia marcescens seems to possess two homoserine dehydrogenases, one NAD-dependent and the other NADP-dependent.The NAD- dependent enzyme is completely repressed by methionine, homoserine or cysteine (at 1 mM), but is not inhibited by any amino acid either singly or in combination.The NADP-dependent enzyme is partially repressed (70-80°/) by the above amino acids.Unlike in E. coli K12 (Patte et al., 1967, 1969), these activities are not associated with aspartokinase, as evidenced during purification and in mutants.Two threonineless mutants of this organism lack homo- seine dehydrogenase activity but possess normal aspartokinase activity.Further details about the purification and properties of the enzymes will be discussed.
Source: Biochemical Journal
DOI: 10.1042/bj1280053pb
Authors: B Seetharam, A N Radhakrishnan
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2318415758