Threonine degradation by Serratia marcescens

Abstract

The wild strain of Serratia marcescens rapidly degraded threonine and formed aminoacetone in a medium containing glucose and urea. Extracts of this strain showed high threonine dehydrogenase and "biosynthetic" threonine deain activities, but no threonine aldolase activity. Threonine dehydrogenase-deficient strain Mu-910 was selected among mutants unable to grow on threonine as the carbon source. This strain did not form aminoacetone from threonine, but it slowly degraded threonine. Strain D-60, deficient in both threonine dehydrogenase and threonine deaminase, was derived from strain Mu-910 and barely degraded threonine. A glycine-requiring strain derived from the wild strain grew in minimal medium containing threonine as the glycine source, whereas a glycinerequiring strain derived from strain Mu-910 did not grow. This indicates that threonine dehydrogenase participates in glycine formation from threonine (via a-amino-,8-ketobutyrate) as well as in threonine degradation to aminoacetone. The following four enzymes are involved in threonine degradation by microorganisms. Threonine dehydrogenase (EC 1.1.1.103) degrades threonine to a-amino-fi-ketobutyrate in Escherichia coli (29), an Arthrobacter species (21), and others (3, 6, 19). Threonine aldolase (EC 2.1.2.1) cleaves threonine to acetaldehyde and glycine in some microorganisms (10, 17, 24, 33).

NADP(+)-dependent D-threonine dehydrogenase from Pseudomonas cruciviae IFO 12047

“…Moreover, D-threonine dehydrogenase showed a low affinity for D-threonine. Thus, it seems unlikely that D-threonine dehydrogenase plays a role in D-threonine degradation, while L-threonine dehydrogenase functions as the first step in L-threonine degradation (3,11,20,22). In the case of glutamate dehydrogenases, the NADP+specific enzymes are implicated in an anabolic function and the NAD+-specific enzymes are responsible for glutamate catabolism (25).…”

Amino acid requirements of Legionella pneumophila

“…for D-serine deaminase synthesis, which use Dserine as the sole nitrogen and carbon source, have been isolated (2). A wild strain of Serratia marcescens used threonine as its sole carbon and nitrogen source when grown on a minimal medium; it did so through a high threonine dehydrogenase activity (7). Peptococcus species can use protein decomposition products (peptones, amino acids) as their sole energy source (11).…”

2-Amino-3-ketobutyrate CoA ligase of Escherichia coli: stoichiometry of pyridoxal phosphate binding and location of the pyridoxyllysine peptide in the primary structure of the enzyme

“…The pathway initiated by L-threonine dehydrogenase (EC 1.1.1.103) has recently been shown to be the primary route for threonine utilization in both eukaryotes [1,2] and prokaryotes [3,4]; threonine dehydrogenase catalyzes the conversion of L-threonine to the putative unstable intermediate, 2-amino-3-ketobutyrate, which has the potential of spontaneously decarboxylating liberating aminoacetone plus CO 2. 2-Arnino-3-ketobutyrate CoA ligase (2-amino-3-ketobutyrate + CoA ~ acetyl-CoA + glycine; 2-amino-3-oxobutanoate glycine-lyase (CoA-acetylating), EC 2.3.1.29) catalyzes the second step in this pathway; the glycine so formed can be utilized by Escherichia coli in a highly efficient alternate pathway for serine biosynthesis [5].…”