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J Biol Chem, Vol. 274, Issue 11, 7039-7042, March 12, 1999

Binding of Cob(II)alamin to the Adenosylcobalamin-dependent Ribonucleotide Reductase from Lactobacillus leichmannii
IDENTIFICATION OF DIMETHYLBENZIMIDAZOLE AS THE AXIAL LIGAND

Christopher C. Lawrence, Gary J. Gerfen^§, Vicente Samano^¶, Rainer Nitsche, Morris J. Robins^¶, János Rétey, and JoAnne Stubbe

From the  Departments of Chemistry and Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, the ^§ Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461,  Lehrstuhl für Biochemie, Institut für Organische Chemie, Universität Karlsruhe, D-76128 Karlsruhe, Germany, and the ^¶ Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602

The ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii catalyzes the reduction of nucleoside 5'-triphosphates to 2'-deoxynucleoside 5'-triphosphates and uses coenzyme B₁₂, adenosylcobalamin (AdoCbl), as a cofactor. Use of a mechanism-based inhibitor, 2'-deoxy-2'-methylenecytidine 5'-triphosphate, and isotopically labeled RTPR and AdoCbl in conjunction with EPR spectroscopy has allowed identification of the lower axial ligand of cob(II)alamin when bound to RTPR. In common with the AdoCbl-dependent enzymes catalyzing irreversible heteroatom migrations and in contrast to the enzymes catalyzing reversible carbon skeleton rearrangements, the dimethylbenzimidazole moiety of the cofactor is not displaced by a protein histidine upon binding to RTPR.

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Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.

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