Electron paramagnetic resonance studies of the methylmalonyl-CoA mutase reaction. Evidence for radical intermediates using natural and artificial substrates as well as the competitive inhibitor 3-carboxypropyl-CoA.
The substrate-dependent homolysis of the cobalt-carbon bond and generation of organic radicals in the coenzyme-B12-methylmalonyl-CoA-mutase complex have been demonstrated by EPR measurements. Both the natural substrate methylmalonyl-CoA, its 13C-substituted analogue and the non-hydrolysable synthetic substrates succinyl-dethia(carba)-CoA, succinyl-dethia(dicarba)-CoA and 4-carboxy-2-oxo-butyl-CoA induced similar but not identical EPR signals. 3-Carboxypropyl-CoA, a novel competitive inhibitor, has been synthesised. Its Ki value of 89 +/- 6 microM was in the same range as the Km of succinyl-CoA. Using [5'-3H]adenosylcobalamin, an enzyme-dependent tritium transfer to the inhibitor has been shown. The enzyme-coenzyme-inhibitor complex also exhibited EPR signals that were less structured and less intensive than the corresponding signals with active substrates. These results prove that the inhibitor also induces cobalt-carbon bond homolysis and undergoes reversible hydrogen transfer but not rearrangement.
Lehrstuhl für Biochemie, Universität Karlsruhe, Germany.
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Zhao
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Abend
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Kunz
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Such
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Rétey
D001667:Binding, Competitive; D002244:Carbon / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry; D003038:Cobamides / Q000378:metabolism; D003065:Coenzyme A / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D008765:Methylmalonyl-CoA Mutase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011424:Propionibacterium / Q000201:enzymology; D013379:Substrate Specificity
C090490:3-carboxypropyl-coenzyme A; D003038:Cobamides; D005609:Free Radicals; D003035:Cobalt; D002244:Carbon; D006859:Hydrogen; D008765:Methylmalonyl-CoA Mutase; C000913:cobamamide; D003065:Coenzyme A