1. Isolates representing seven bacterial genera capable of growth on L-threonine medium, and possessing high L-threonine 3-dehydrogenase activity, were examined to elucidate the catabolic route. 2. The results of growth, manometric and enzymic experiments indicated the catabolism of L-threonine by cleavage to acetyl-CoA plus glycine, the glycine being further metabolized via L-serine to pyruvate, in all cases. No evidence was obtained of a role for aminoacetone in threonine catabolism or for the metabolism of glycine by the glycerate pathway. 3. The properties of a number of key enzymes in L-threonine catabolism were investigated. The inducibly formed L-threonine 3-dehydrogenase, purified from Corynebacterium sp. B6 to a specific activity of about 30-35 mumol of product formed/min per mg of protein, exhibited a sigmoid kinetic response to substrate concentration. The half-saturating concentration of substrate, [S]0.5, was 20mM and the Hill constant (h) was 1.50. The Km for NAD+ was 0.8mM. The properties of the enzyme were studied in cell-free extracts of other bacteria. 4. New assays for 2-amino-3-oxobutyrate-CoA ligase were devised. The Km for CoA was determined for the first time and found to be 0.14mM at pH8, for the enzyme from Corynebacterium sp. B6. Evidence was obtained for the efficient linkage of the dehydrogenase and ligase enzymes. Cell-free extracts all possessed high activities of the inducibly formed ligase. 5. L-Serine hydroxymethyltransferase was formed constitutively by all isolates, whereas formation of the ‘glycine-cleavage system’ was generally induced by growth on L-threonine or glycine. The coenzyme requirements of both enzymes were established, and their linked activity in the production of L-serine from glycine was demonstrated by using extracts of Corynebacterium sp. B6. 6. L-Serine dehydratase, purified from Corynebacterium sp. B6 to a specific activity of about 4mumol of product formed/min per mg of protein, was found to exhibit sigmoid kinetics with an [S]0.5 of about 20mM and h identical to 1.4. Similar results were obtained with enzyme preparations from all isolates. The enzyme required Mg2+ for maximum activity, was different from the L-threonine dehydratase also detectable in extracts, and was induced by growth on L-threonine or glycine.
Skip Nav Destination
Follow us on Twitter @Biochem_Journal
Article navigation
May 1976
-
Cover Image
Cover Image
- PDF Icon PDF LinkFront Matter
- PDF Icon PDF LinkTable of Contents
- PDF Icon PDF LinkAdvertising
Research Article|
May 15 1976
Bacterial catabolism of threonine. Threonine degradation initiated by L-threonine-NAD+ oxidoreductase
S C Bell;
S C Bell
1Department of Biochemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, U.K.
Search for other works by this author on:
J M Turner
J M Turner
1Department of Biochemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, U.K.
Search for other works by this author on:
Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1976 London: The Biochemical Society
1976
Biochem J (1976) 156 (2): 449–458.
Citation
S C Bell, J M Turner; Bacterial catabolism of threonine. Threonine degradation initiated by L-threonine-NAD+ oxidoreductase. Biochem J 15 May 1976; 156 (2): 449–458. doi: https://doi.org/10.1042/bj1560449
Download citation file:
Sign in
Don't already have an account? Register
Sign in to your personal account
You could not be signed in. Please check your email address / username and password and try again.
Could not validate captcha. Please try again.
Biochemical Society Member Sign in
Sign InSign in via your Institution
Sign in via your InstitutionGet Access To This Article
Cited By
Follow us on Twitter @Biochem_Journal
Open Access for all
We offer compliant routes for all authors from 2025. With library support, there will be no author nor reader charges in 5 journals. Check here |
![]() View past webinars > |