Prev. Article Next Article Table of Contents

Article

Magnetic Field Effect Studies Indicate Reduced Geminate Recombination of the Radical Pair in Substrate-Bound Adenosylcobalamin-Dependent Ethanolamine Ammonia Lyase

Supporting Info

Alex R. Jones,^†^‡ Sam Hay,^† Jonathan R. Woodward,*^‡ and Nigel S. Scrutton*^†;

Contribution from the Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, 131 Princess Street, Manchester, M1 7DN, U.K., and Department of Chemistry, University of Leicester, University Road, Leicester, LE1 7RH, U.K.

J. Am. Chem. Soc., 2007, 129 (50), pp 15718–15727

DOI: 10.1021/ja077124x

Publication Date (Web): November 28, 2007

†

University of Manchester.

‡

University of Leicester.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

, jrw16@le.ac.uk, ; , nigel.scrutton@manchester.ac.uk

Abstract

The apparent conflict between literature evidence for (i) radical pair (RP) stabilization in adenosylcobalamin (AdoCbl)-dependent enzymes and (ii) the manifestation of magnetic field sensitivity due to appreciable geminate recombination of the RP has been reconciled by pre-steady-state magnetic field effect (MFE) investigations with ethanolamine ammonia lyase (EAL). We have shown previous stopped-flow MFE studies to be insensitive to magnetically induced changes in the net forward rate of C−Co homolytic bond cleavage. Subsequently, we observed a magnetic-dependence in the continuous-wave C−Co photolysis of free AdoCbl in 75% glycerol but have not done so in the thermal homolysis of this bond in the enzyme-bound cofactor in the presence of substrate. Consequently, in the enzyme-bound state, the RP generated upon homolysis appears to be stabilized against the extent of geminate recombination required to observe an MFE. These findings have strong implications for the mechanism of RP stabilization and the unprecedented catalytic power of this important class of cobalamin-dependent enzymes.

View: Full Text HTML | Hi-Res PDF