The aim of this project is to expand or complete the identification of all the proteins in Escherichia coli necessary for anaerobic electron (or hydrogen) transfer from sn-glycerol 3-phosphate (G3P) to fumarate or nitrate with attendant energy generation and to find out which of these components are shared in common in other chains of electron transport. E. coli produces two specific membrane associated enzymes: aerobic G3P dehydrogenase and anaerobic G3P dehydrogenase. The former permits aerobic growth on glycerol and anaerobic growth on glycerol and nitrate. The latter permits anaerobic growth on glycerol and fumarate or glycerol and nitrate. Starting with a strain possessing only the first enzyme, mutants that lack the ability to growh anaerobically on glycerol and nitrate will be selected. Starting with a strain possessing only the second enzyme, mutants that lack the ability to grow anaerobically on glycerol and fumarate or glycerol and nitrate will be selected. These mutants will be tested for their ability to grow on other carbon sources requiring anaerobic exogenous hydrogen acceptors such as nitrate and fumarate to check the specificity of their genetic defects. The mutants will also be examined biochemically for the presence or absence of membrane proteins such as the cytochromes or members of the fumarate reductase or nitrate reductase complexes. The mutation sites will be mapped to determine whether unknown gene products are involved.