The reversible conversion of molecular hydrogen to protons and electrons is a central reaction in the global biological energy cycle. Hydrogenase enzymes catalyze a large percentage of this reaction, and thus a more detailed understanding of these enzymes is of wide interest in biotechnology, biochemistry, and energy sciences. These enzymes are present in various microorganisms and function either in the utilization of Hydrogen as a growth substrate (Hydrogen uptake) or in certain anaerobic bacteria to dispose of excess electrons by combining them with protons to form Hydrogen. The X-ray crystal structure of the iron-only hydrogenase from the anaerobic soil microorganism Clostridium pasteurianum (CpI) was determined to 1.8 angstrom resolution in the group. CpI is a highly complex protein containing twenty iron atoms arranged into five individual metal cluster assemblies. The active site cluster or "H cluster" is structurally unprecedented among previously characterized biological iron-sulfur clusters. Our ongoing hydrogenase research involves probing the mechanism of hydrogenases by biochemical, structural, and physical methods. We are collaborating with Prof. Joan Broderick of the department on the mechanism of the H cluster. In addition, we are collaborating with investigators throughout the world, probing avenues to produce hydrogen efficiently as renewable energy. This work includes a collaboration here at MSU with Trevor Douglas of the department on the design, synthesis, and characterization of hydrogen producing biomimetic materials.