Small structural perturbations in the enzyme isocitrate dehydrogenase (IDH) were made in order to evaluate the contribution of precise substrate alignment to the catalytic power of an enzyme. The reaction trajectory of IDH was modified (i) after the ...
Small structural perturbations in the enzyme isocitrate dehydrogenase (IDH) were made in order to evaluate the contribution of precise substrate alignment to the catalytic power of an enzyme. The reaction trajectory of IDH was modified (i) after the adenine moiety of nicotinamide adenine dinucleotide phosphate was changed to hypoxanthine (the 6-amino was changed to 6-hydroxyl), and (ii) by replacing Mg2+, which has six coordinating ligands, with Ca2+, which has eight coordinating ligands. Both changes make large (10(-3) to 10(-5)) changes in the reaction velocity but only small changes in the orientation of the substrates (both distance and angle) as revealed by cryocrystallographic trapping of active IDH complexes. The results provide evidence that orbital overlap produced by optimal orientation of reacting orbitals plays a major quantitative role in the catalytic power of enzymes.
Related Citations:
Structure of Isocitrate Dehydrogenase with Isocitrate, Nicotinamide Adenine Dinucleotide Phosphate, and Calcium at 2.5-A Resolution: A Pseudo-Michaelis Ternary Complex Stoddard, B.L.,Dean, A.,Koshland Junior, D.E. (1993) Biochemistry 32: 9310
Determinants of Cofactor Specificity in Isocitrate Dehydrogenase: Structure of an Engineered Nadp+--> Nad+ Specificity-Reversal Mutant Hurley, J.H.,Chen, R.,Dean, A.M. (1996) Biochemistry 35: 5670
Organizational Affiliation:
Department of Molecular and Cell Biology, Stanley Hall, University of California, Berkeley, CA 94720, USA.
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