604-98-8Relevant articles and documents
Tyrosine 89 accelerates Co-carbon bond homolysis in methylmalonyl-CoA mutase
Vlasie, Monica D.,Banerjee, Ruma
, p. 5431 - 5435 (2003)
The contribution of the active-site residue, Y89, to the trillion-fold acceleration of Co-carbon bond homolysis rate in the methylmalonyl-CoA mutase-catalyzed reaction has been evaluated by site-directed mutagenesis. Conversion of Y89 to phenylalanine or alanine results in a 103-fold diminution of kcat and suppression of the overall kinetic isotope effect. The spectrum of the enzyme under steady-state conditions reveals the presence of AdoCbl but no cob(II)alamin. Together, these results are consistent with homolysis becoming completely rate determining in the forward direction in the two mutants and points to the role of Y89 as a molecular wedge in accelerating Co-carbon bond cleavage.
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Simon,Shemin
, p. 2520 (1953)
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Novel coenzyme B12-dependent interconversion of isovaleryl-CoA and pivalyl-CoA
Cracan, Valentin,Banerjee, Ruma
scheme or table, p. 3723 - 3732 (2012/06/15)
5′-Deoxyadenosylcobalamin (AdoCbl)-dependent isomerases catalyze carbon skeleton rearrangements using radical chemistry. We have recently characterized a fusion protein that comprises the two subunits of the AdoCbl-dependent isobutyryl- CoA mutase flanking a G-protein chaperone and named it isobutyryl-CoA mutase fused (IcmF). IcmF catalyzes the interconversion of isobutyryl-CoA and n-butyryl-CoA, whereas GTPase activity is associated with its G-protein domain. In this study, we report a novel activity associated with IcmF, i.e. the interconversion of isovaleryl-CoA and pivalyl-CoA. Kinetic characterization of IcmF yielded the following values: a Km for isovaleryl-CoA of 62 ± 8 μM and Vmax of 0.021 ± 0.004 μmol min-1 mg-1 at 37 ° C. Biochemical experiments show that an IcmF in which the base specificity loop motif NKXD is modified to NKXE catalyzes the hydrolysis of both GTP and ATP. IcmF is susceptible to rapid inactivation during turnover, and GTP conferred modest protection during utilization of isovaleryl-CoA as substrate. Interestingly, there was no protection from inactivation when either isobutyryl-CoA or n-butyryl-CoA was used as substrate. Detailed kinetic analysis indicated that inactivation is associated with loss of the 5′-deoxyadenosine moiety from the active site, precluding reformation of AdoCbl at the end of the turnover cycle. Under aerobic conditions, oxidation of the cob(II)alamin radical in the inactive enzyme results in accumulation of aquacobalamin. Because pivalic acid found in sludge can be used as a carbon source by some bacteria and isovaleryl- CoA is an intermediate in leucine catabolism, our discovery of a new isomerase activity associated with IcmF expands its metabolic potential.