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A rapid equilibrium random ter-ter kinetic mechanism is established for the synthetase from Escherichia coli by initial velocity kinetics and patterns of linear inhibition by IMP, adenosine 5' -(beta, gamma-imido) triphosphate (AMP-PNP), and maleate. Inhibition by IMP and maleate is consistent with a chemical mechanism for phosphoribosylaminoidazolesuccinocarboxamide (SAICAR) synthetase that parallels that of adenylosuccinate synthetase.

Tryptophan fluorescence has shown the conformational state of a dynamic loop in recombinant porcine fructose-1,6-bisphosphatase. The kinetic and structural properties and conformational response of the Trp57 mutant of FBPase to various metal cations and physiologically relevant ligands have been found.

Crystal structures of fructose 1,6-bisphosphatase (FBPase) have been studied and a mechanism proposed for catalysis and allosteric inhibition seen in product complexes. Competition was seen between AMP and divalent cations in crystal structure of metal-product complexes of FBPase.

Research was conducted to examine the properties of a mutant hexokinase I, in which residues critical to the stability of the dimer have been changed by directed mutation. The resulting mutant was shown to exist in solution as a monomer at elevated concentrations of enzyme, either in the presence or absence of ligands. Results indicate that the allosteric regulation of catalysis in monomeric hexokinase I probably involves an interface between the N- and C-terminal halves, similar to ones defined by crystal structures.

A study was conducted to analyze the crystal structures of wild-type and mutant forms of adenylosuccinate synthetase from Escherichia coli. The structures supported multiple roles for Asp13 and His41 in a proposed catalytic mechanism of the synthetase. Results indicated that the mutation of Asp13 to alanine eliminates measurable activity. Findings also showed that the structures can function together as catalytic acids in the formation of adenylosuccinate.

A study was conducted to characterize the crystallography of wild-type fructose-1,6-bisphosphatase (FBPase) in a complex of fructose 6-phosphate, phosphate and Zn2+. Escherichia coli was utilized to express ion recombinant wild-type porcine FBPase. Results indicated catalysis mechanisms when Asp121 serves as a catalytic base for the alpha-anomer while Glu280 functions as a catalytic base for the beta-anomer.

A crystal structure of adenylosuccinate synthetase from Escherichia coli, complexed with 5'-phosphate, GDP, HPO(sub 4)(super 2-), Mg2+ and hadacidin at 100 K, was refined to an Rfactor of 0.195 against data to 2.6 angstroms resolution. Findings revealed that hydantocidin 5'-phosphate, GDP, HPO(sub 4)(super 2-) and Mg2+ may represent a group of synergistic inhibitors even more effective than the combination of IMP, GPD, NO3- and Mg2+.

The extent of stereochemical distortion as a function of pH for two related pseudotetrasaccharide inhibitors, acarbose and D-gluco-dihydrocarbose, were analyzed by high-resolution crystallographic studies of glucoamylase. Distortions in the nonreducing end of ligands bound to the active site of glucoamylase are relatively small, indicating that electrostatic charge stabilization of the transition state may be the dominant factor in promoting the development of a glucopyranosyl cation in the active site of glucoamylase.

A study analyzes the role of arginines 54 and 305, aspartic acid 309, and tryptophan 317 located at subsites 1 and 2 in glucoamylase in catalysis and substrate recognition. Arg305 is a key determinant in glucoamylase (GA) for the recognition of alpha-1,4-linked substrates. In case of Trp317 which stacks with Arg305, any minute structural change effects both the substrate recognition ability and the protein stability. These mutants have reduced stability at elevated temperature and in guanidine hydrochloride.

Rearranging the hydrogen bond network helps understand the residual activity at a catalytic subunit in a Glu400-Gln mutant of glycosylase. Gln400 exhibits hydrogen bonding with the invariant Tyr48. The enzyme activity of Tyr48 yield Trp and Glu400 yield Gln glucoamylases is high below pH 4.0, indicating the absence of wild-type catalytic base function and low binding affinity at subsite 2. Glu400 is involved in catalysis, as confirmed by the Glu400 yield Gln mutant while the Tyr48 mutation indicates functional association with Glu400 and its requirement for active site geometry and intermediate stabilization.