The following methionine catabolism pathway is widespread. The enzyme from Pseudomonas putida has been purified and characterized. One product of the enzyme reaction, methanethiol, is sufficiently volatile to be significantly lost to the biological system by the organism generating it. Its further metabolism is often carried out by other bacteria. For example, it might be further methylated to dimethyl sulfide, as in the Dimethyl Sulfoxide & Organosulfide Cycle Map.
The following threonine catabolism pathway is initiated by threonine dehydratase which has been cloned and sequenced from Escherichia coli (Datta et al, 1987). The enzyme is induced anaerobically and catalyzes the transformation of L-threonine to ammonia and 2-ketobutyrate. The latter may be further converted into propionyl-CoA and formate by 2-ketobutyrate formate-lyase which is also found in Escherichia coli, as described by Hesslinger et al (1998).
The following is a text-format methionine and threonine pathway map. Follow the links for more information on compounds or reactions. This map is also available in graphic (5k) format.
Methionine L-Threonine
Pseudomonas putida Escherichia coli
| |
| |
| methionine | L-threonine
| gamma-lyase | dehydratase
| |
v |
Methanethiol + 2-ketobutyrate <-------+
| |
| |
| |
| |
| |
v v
to the to the
DMSO Pathway 1-Aminocyclopropane-
1-carboxylate Pathway
Page Author(s): Hugh McTavish and Zhifu Sun
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