Summary: The pyruvate dehydrogenase complex from the thermophilic bacterium was purified by Triton X-100 extraction and chromatography on phenyl-Sepharose CL-4B and HPLC-hydroxyapatite. The electrophoretic pattern of the purified enzyme complex was similar to that of the enzyme complex from , with four bands: the α-chain ( 39600) and β-chain ( 37500) of the pyruvate dehydrogenase component, the dihydrolipoamide acetytransferase component ( 58500) and the dihydrolipoamide dehydrogenase component ( 53900). Antibodies against the purified pyruvate dehydrogenase complex cross-reacted with the enzyme complex from and, to a minor extent, with that from bovine heart. No cross-reactivity could be observed with the enzyme complex from The enzyme complex had a temperature maximum at 72°C. 2-Oxobutyrate was a poor substrate and other 2-oxoacids were competitive inhibitors of the overall reaction. Long-chain 2-oxoacids showed a greater inhibitory effect, possibly caused by hydrophobic interactions. GTP inhibited the enzyme activity. Regulation of the pyruvate dehydrogenase complex from by allosteric mechanisms or by reversible phosphorylation could not be demonstrated.


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