PMID:8745412

Citation	Dean, AM, Shiau, AK and Koshland, DE Jr (1996) Determinants of performance in the isocitrate dehydrogenase of Escherichia coli. Protein Sci. 5:341-7
Abstract	The substrate specificity of the NADP-dependent isocitrate dehydrogenase of Escherichia coli was investigated by combining site-directed mutagenesis and utilization of alternative substrates. A comparison of the kinetics of the wild-type enzyme with 2R-malate reveals that the gamma-carboxylate of 2R,3S-isocitrate contributes a factor of 12,000,000 to enzyme performance. Analysis of kinetic data compiled for 10 enzymes and nine different substrates reveals that a factor of 1,650 can be ascribed to the hydrogen bond formed between S113 and the gamma-carboxylate of bound isocitrate, a factor of 150 to the negative charge of the gamma-carboxylate, and a factor of 50 for the gamma-methyl. These results are entirely consistent with X-ray structures of Michaelis complexes that show a hydrogen bond positions the gamma-carboxylate of isocitrate so that a salt bridge can form to the nicotinamide ring of NADP.
Links	PubMed PMC2143340 Online version:10.1002/pro.5560050218
Keywords	Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Escherichia coli/enzymology; Escherichia coli/genetics; Hydrogen Bonding; Isocitrate Dehydrogenase/chemistry; Isocitrate Dehydrogenase/genetics; Isocitrate Dehydrogenase/metabolism; Isocitrates/metabolism; Kinetics; Malates/metabolism; Models, Molecular; Mutagenesis, Site-Directed; NADP/metabolism; Substrate Specificity; Tartrates/metabolism
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