Acetohydroxy acid synthase (AHAS) is a key regulatory enzyme in the pathway of branched-chain amino acid biosynthesis. Because these amino acids constitute about 25% of the dry weight of protein in living tissue, this pathway is of quantitative significance in many microorganisms and plants. The AHAS from a methane-producing archaebacterium, Methanococcus aeolicus, is being purified by standard techniques, and its chemical and physical properties determined. The gene(s) for this enzyme is being cloned and DNA sequencing begun. A number of major questions are addressed by this research. Are anabolic enzymes in archaebacteria homologous to the eubacterial and eucaryotic enzymes? Is the archaebacterial AHAS homologous to any pyruvate-utilizing enzymes found in catabolic pathways including the pyruvate oxidase from Escherichia coli? Are the flavin and herbicide binding sites conserved in AHASs from diverse origins?%%% Methanogenic bacteria are an economically important group belonging to the third major kingdom of life, the archaebacteria. They catalyze the last step in the anaerobic decomposition of organic matter where 95% of the combustion energy is conserved in the methane formed. Complex biological polymers can be converted to methane, a clean fuel already in wide use. Therefore, there is great potential for exploitation of this fermentation in waste treatment. Furthermore, methane is the second most abundant carbon- containing gas in the atmosphere. Its concentration has been increasing for the last several hundred years and may contribute to the greenhouse effect and global warming. Thus these microorganisms are intimately associated with major global processes of our planet. These studies on methanogen physiology and regulation will facilitate their exploitation for useful purposes and help gauge environmental practices.***//
