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
Y. Zhao et al., 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, European journal of biochemistry, 225(3), 1994, pp. 891-896
The substrate-dependent homolysis of the cobalt-carbon bond and genera
tion of organic radicals in the coenzyme-B-12-methylmalonyl-CoA-mutase
complex have been demonstrated by EPR measurements. Both the natural
substrate methylmalonyl-CoA, its C-13-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 i
nhibitor, has been synthesised. Its K-i value of 89+/-6 mu M was in th
e same range as the K-m of succinyl-CoA. Using [5'-H-3] adenosylcobala
min, an enzyme-dependent tritium transfer to the inhibitor has been sh
own. The enzyme-coenzyme-inhibitor complex also exhibited EPR signals
that were less structured and less intensive than the corresponding si
gnals with active substrates. These results prove that the inhibitor a
lso induces cobalt-carbon bond homolysis and undergoes reversible hydr
ogen transfer but not rearrangement.