The goal of this proposal is to gain a deeper understanding of enzyme catalysis. Our aims are:(a), to see why particular functional groups in enzymes are ideal for particular catalytic tasks:(b), to recognize the usefulness of particular structural motifs; (c), to be able to predict the kinetic consequences of small structural changes; and (d), to see if the kinetic properties of enzymes have been refined for each metabolic niche. We shall continue to exploit triosephosphate isomerase, which is a splendid test-bedford the evaluation of important elements of enzyme catalysis. Site-directed changes will be use d to probe particular enzyme features and functionalities, and the technique of random mutagenesis will be further developed to explore the nature of the sequence 'landscape' in the generation of catalytic potency. In these pursuits, answers to the following questions will be sought: Do enzymes use bidentate bases and acids to catalyze proton shifts merely by side-chain rotation? Can we test recent theoretical statements about the importance of charges that are relatively remote from the active site? How does an alpha-helix fine-tune the pKa value of an ionizing group, or affect the strength of substrate binding? What is the movement of 1 A worth kinetic terms? Can equivalent rate accelerations be achieved wit a different set of catalytic groups? Are enzymes from organisms adapted to lave a t-1.6oC or + 105oC predictably different? Answers to these and other questions will provide a firmer basis from which the catalytic activity of enzymes can become a predictive science.