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4) Symposium Posters | Main^

P5. W0078: Catalysis in Arginine Kinase Investigated through Structure, Mutagenesis, and Kinetics.

2000 American Crystallographi Association Meeting, July 22-27, St. Paul, MN.
Pamela S. Pruett, Arezki Azzi, James Gattis, Thayumanasamy Somasundaram, Ross Ellington, and Michael Chapman.
Institute of Molecular Biophysics, Florida State Univ., Tallahassee, FL 32306, USA

The immediate source of energy for many cellular processes is the hydrolysis of ATP to ADP and phosphate, so it is to the cell's advantage to maintain a steady concentration of ATP. The phosphagen kinase family of enzymes catalyzes this hydrolysis as well as the regeneration of ATP by transfer to ADP of a phosphate from one of the phosphorylated guanidino "energy storage" molecules such as phosphocreatine or phosphoarginine. As a bidirectional catalyst, arginine kinase is an excellent paradigm for questions fundamental to the enzyme catalysis of those enzymes that have multiple substrates. In the 1970's, Jencks and Koshland proposed that multi-substrate enzymes might differ from unimolecular paradigms because the alignment of substrates could be an important component of catalysis. For the first time there is a high resolution structure of a bimolecular transition state complex, that of arginine kinase ( Zhou, et. al., PNAS, 1998, 95(15):8449-54). Based on this structure, amino acid residues predicted to play a role in binding and/or catalysis have been changed using site-directed mutagenesis. These mutations will allow an analysis of the correlation between the precision of substrate alignment and catalysis. We will present kinetic analysis and structural characteristics of some of these mutants.

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