The study of the catalytic mechanisms, substrate specificities and the regulation of enzymes and investigation of the roles specific enzymes play in the metabolic pathways essential to life. Specific topics within this focus area include the expression and purification of enzymes, the physical and kinetic characterization of enzymes, the use of natural and synthetic substrate analogs and inhibitors to probe questions of catalytic mechanism and specificity to direct rational drug design, and the use of site-directed mutagenesis and other molecular biological methods to identify and map residues important in catalysis or substrate binding within the active site of enzymes. Other topics in this area include the use of proteomics to elucidate evolutionary relationships among related proteins, analysis of structure-function relationships in enzymes, and the analysis of metabolic fluxes using inhibitors and metabolic tracer technologies.