Bacterial catabolism of threonine. Threonine degradation initiated by l-threonine hydro-lyase (deaminating) in a species of Corynebacterium

Abstract

1. Three bacterial isolates capable of growth on L-threonine medium only when supplemented with branched-chain amino acids, and possessing high L-threonine dehydratase activity, were examined to elucidate the catabolic route for the amino acid. 2. Growth, manometric, radiotracer and enzymic experiments indicated that L-threonine was catabolized by initial deamination to 2-oxobutyrate and thence to propionate. No evidence was obtained for the involvement of L-threonine 3-dehydrogenase or L-threonine aldolase in threonine catabolism. 3. L-Threonine dehydratase of Corynebacterium sp. F5 (N.C.I.B. 11102) was partially purified and its kinetic properties were examined. The enzyme exhibited a sigmoid kinetic response to substrate concentration. The concentration of substrate giving half the maximum velocity, [SO.5], was 40mM and the Hill coefficient (h) was 2.0. L-Isoleucine inhibited enzyme activity markedly, causing 50% inhibition at 60,UM, but did not affect the Hill constant. At the fixed L-threonine concentration of 10mM, the effect of L-valine was biphasic, progressive activation occurring at concentrations up to 2mM-L-valine, but was abolished by higher concentrations. Substrate-saturation plots for the L-valine-activated enzyme exhibited normal MichaelisMenten kinetics with a Hill coefficient (h) of 1.0. The kinetic properties of the enzyme were thus similar to those of the 'biosynthetic' isoenzyme from Rhodopseudomonas spheroides rather than those of the enteric bacteria. 4. The synthesis of L-threonine dehydratase was constitutive and was not subject to multivalent repression by L-isoleucine or other branched-chain amino acids either singly or in combination. 5. The catabolism of L-threonine, apparently initiated by a 'biosynthetic' L-threonine dehydratase in the isolates studied, depended on the concomitant catabolism of branched-chain amino acids. The biochemical basis of this dependence appeared to lie in the further catabolism of 2-oxobutyrate by enzymes which required branched-chain 2-oxo acids for their induction.

Identification of glyA (Encoding Serine Hydroxymethyltransferase) and Its Use Together with the Exporter ThrE To Increase l -Threonine Accumulation by Corynebacterium glutamicum

“…There are indications that a threonine 3-dehydrogenase may be responsible for such reaction in Corynebacteriaceae (3). In Corynebacterium sp.…”

N-Carbamoylputrescine Amidohydrolase of Bacteroides thetaiotaomicron, a Dominant Species of the Human Gut Microbiota

“…It is noteworthy that the reaction catalyzed by NCPAH was inhibited significantly more strongly (over 80%) by spermidine, the product of a two-step later reaction than by putrescine, the direct product. Threonine dehydrogenase is known to be 50% feedback inhibited by its reaction products [ 51 ]. However, NCPAH was more inhibited by the reaction product compared to threonine dehydrogenase.…”

Catabolic Pathways of Coryneforms, Nocardias, and Mycobacteria

“…(18), and threonine catabolism has been studied in a species of Coryne bacterium (13,14) and a species of Arthrobacter (110). Highly active threo nine dehydrogenases were found during growth on threonine.…”