Identification of the dadX gene coding for the predominant isozyme of alanine racemase in Escherichia coli K12

Abstract

Evidence is presented that alanine racemase activity in E. coli K12 is due to two distinct gene products. The predominant isozyme is inducible by either alanine stereoisomer and repressible by glucose. The gene dadX coding for its structure is located by the dadA gene determining the structure of D-amino acid dehydrogenase. The regulatory site for the expression of both genes, dadR, is located on the other side of dadA. The orientation of the dad operon established by multiple-point crosses and deletion mapping is as follows: fadR ...dadRAX ...hemA. The dadX alanine racemase activity is unusually refractory to changes of incubation temperature. It differs strikingly from that of the other isozyme, probably the product of the alr gene. The latter isozyme shows a typical dependence upon incubation temperature. The synthesis of alr alanine racemase is constitutive in respect of both alanine and glucose. In dadX mutants, in which alanine racemase activity equals only 15% of that in wild-type cells grown in the absence of an inducer or catabolite repressor, the dad operon cannot be induced by D-alanine. We presume, therefore, that L-alanine is involved more directly than D-alanine in dad operon regulation.

Peptidoglycan biosynthesis in Escherichia coli: variations in the metabolism of alanine and D-alanyl-D-alanine

“…In late-stationary-phase cells high levels of all three activities remained; the The specific activities of &nine racemase, D-alagreatescvariation observed was a 40% decrease in ligase nine : D-alanine ligase and D-alanyl-D-alanine-adding activity. As previously described (Wijsman, 1972; enzyme were compared under various growth conditions Lambert lit Neuhaus, 1972a;Wild et al, 1985), growth (Table 2). In cells grown on minimal medium containing on D-or L-alanine as carbon source led to a great increase a carbon source other than alanine or puruvate, fairly in alanine racemase activity (Table 2).…”

“…A racemase activity converts L-alanine into D-alanine and a ligase activity catalyses the formation of D-alanyl-D-alanine from D-alanine (Rogers et al, 1980). In Escherichia coli this pathway has already been investigated to some extent (Lambert & Neuhaus, 1972a;Lugtenberg, 1972;Ishiguro & Ramey, 1978;Lugtenberg & van Schijndelvan Dam, 1973;Wild et al, 1985). The alanine racemase activity in E. coli is due to two distinct gene products (Wild et al, 1985).…”

“…In Escherichia coli this pathway has already been investigated to some extent (Lambert & Neuhaus, 1972a;Lugtenberg, 1972;Ishiguro & Ramey, 1978;Lugtenberg & van Schijndelvan Dam, 1973;Wild et al, 1985). The alanine racemase activity in E. coli is due to two distinct gene products (Wild et al, 1985). The predominant racemase, coded by the dadX gene, is inducible by alanine and repressible by glucose (Wild et al, 1985).…”

“…The alanine racemase activity in E. coli is due to two distinct gene products (Wild et al, 1985). The predominant racemase, coded by the dadX gene, is inducible by alanine and repressible by glucose (Wild et al, 1985). Homogeneous preparations of this activity were obtained from two strains of E. coli (Lambert & Neuhaus, 19723;Wang & Walsh, 1978).…”

“…Tel. (1) 69417971; fax (1) 69853715. glucose (Wijsman, 1972;Wild et al, 1985). More recently it has been established that there are two distinct genes (ddlA and ddlB) encoding D-alanine : D-alanine ligases (Robinson et al, 1986;Zawadzke et al, 1991).…”