Corrinoid enzyme

Coulter C, JTG Hamilton, WC McRoberts, L Kulakov, MJ Larkin, DB Harper (1999) Halomethane bisulfite/halide ion methyltransferase, an unusual corrinoid enzyme of environmental significance isolated from an aerobic methylotroph using chloromethane as the sole carbon source. Appl Environ Microbiol 65 4301-4312. 

Coulter C, Hamilton JTG, McRoberts WC, Kulakov L, Larkin MJ, Harper DB (1999) Halomethane Bisulfide/Halide Ion Methyltransferase, an Unusual Corrinoid Enzyme of Environmental Significance Isolated from an Aerobic Methyltroph Using Chloromethane as the Sole Carbon Source. Appl Environ Microbiol 65 4301... 

Quahtative information on the structme of the colored corrinoids in solution can be extracted rapidly from UV/Vis and CD spectra most of the spectroscopic features can be rationalized nowadays by comparison with theoretically calculated spectra. For more precise constitutional information, some of the newly developed methods of mass spectrometry allow the analysis even of the involatile Bi2-derivatives. Modem one-and two-dimensional proton, carbon, nitrogen, and phosphoms NMR spectroscopy has proven a powerful instrument for the delineation of the stmcture of diamagnetic cobalt-corrins in solution. ESR-spectroscopy has given important information on paramagnetic corrinoid Co"-complexes, whether in frozen solutions or bound in corrinoid enzymes. X-ray adsorption fine spectroscopy (EXAFS) spectroscopy and vibrational (IR and Raman) spectroscopy are other spectroscopic techniques used more frequently now in the B12 field. 

Aside from the Bi2-binding and transporting proteins, three major classes of corrinoid enzymes are known methyltransferases, coenzyme B12 utilizing enzymes, and corrinoid dehalogenases. The coenzyme B12 utilizing enzymes can be classified further as carbon skeleton mutases, dehydratases, deaminases, and ribonucleotide reductase. Members of all classes of the Bi2-enzymes are important in microorganisms. In human and animal metabolism B12-binding proteins, the methyl transferase methionine synthase and methylmalonyl-CoA-mutase (MMCM) play essential roles. 

Fig. 4. Summary of reactions of methyl-cobalt-corrinoids involved in the formation of methane and the synthesis of acetate from COi. This figure is diagrammatic only. The CHa-Co-corrinoid-enzyme complexes involved in methane formation and acetate synthesis are difierent from one another.

In the fermentation the sequence occurs as shown in Fig. 2. The carboxyl is transferred from methylmalonyl CoA to pyruvate yielding oxalacetate and propionyl CoA. The oxalacetate is reduced to sucdnate. CoA then is transferred from the propionyl CoA to sucdnate and the methylmalonyl CoA is regenerated from the resulting sucdnyl CoA. The net result of this cycle is the conversion of pyruvate to propionate. In studying the cycle we investigated the conversion of sucdnyl CoA to methylmalonyl CoA by the corrinoid enzyme, methylmalonyl CoA mutase, but space limitation prevents discussion of this interesting enzyme. 

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