The enzyme hydrogenase, found in bacteria and algae, catalyzes the activation of molecular hydrogen which leads to the uptake or evolution of H2 gas. The enzyme is a nickel containing iron sulfur protein, and its substrates, H+ and H2, are the simplest ions and molecules. H2 is cleaved reversibly by an enzyme hydride and a proton. The interaction between enzyme and substrate can be studied with different isotopic and spin isomers of the substrates as well as with suitable electron acceptors and donors. The enzyme plays an important role in the anaerobic metabolism of many microorganisms where it is involved in a variety of fermentative reactions, nitrogen fixation, methane formation, and hydrogen evolution. Coupling the enzyme with chloroplast can lead to the photoproduction of H2 and O2, ideal fuel sources, from water in visible light.
E.coli synthesizes three hydrogenase isoenzymes, each of which are composed of two large catalytic subunits and two small subunits required for electron transport to and from substrates. There is strong homology in the amino acid sequence of the three isoenzymes, though they are distinguishable immunologically and in their biological role.
This laboratory is presently studying the regulatory genes involved in synthesis of all three hydrogenases in E.coli. The approaches being used involve isolation of mutant strains of bacteria with altered hydrogenase activities, defining the mutation and cloning the genes which restore activity to the mutant strains. This has led to the isolation of a number of regulatory genes and a gene involved in the incorporation of nickel into the enzyme. Some of these genes are essential for transcription of the structural genes while others lead to constitutive synthesis of hydrogenase at high levels. The roles of these genes and their products are under investigation.