Our laboratory uses three approaches to study protein structure and function: x-ray crystallography for protein structure determination, recombinant DNA methods to generate mutant proteins, and biochemical methods for characterization of both mutant and native proteins. The primary focus is on heme containing enzymes and related redox proteins. Protein engineering is used to study structure-function relationships and address the question of how these enzymes activate molecular oxygen and peroxides and how interprotein electron transfer reactions operate. For example, does the protein participate in the electron transfer process and how are the oxidizing equivalents of oxygen/peroxide stored in the active site? A longer range goal is to use structural information and mutagenesis to design novel redox catalysts. To increase the structural data base required, new peroxidase and P450 structures are being determined using diffraction methods. More recently, studies on nitric oxide synthase (NOS) have been initiated. NOS is responsible for producing nitric oxide, a critically important regulatory molecule involved in the immune, nervous, and cardiovasuclar systems. The design of isoform specific inhibitors is an important practical goal in NOS research. Toward this end, the lab has succeeded in crystallizing the heme domain of the three main NOS isoforms and the structure of one solved to 1.9A resolution. This opens the way for structure based drug design.