Anaerobic energy-yielding reaction associated with transhydrogenation from glycerol 3-phosphate to fumarate by an Escherichia coli system

A particulate subcellular fraction from Escherichia coli K-12 induced in anaerobic sn-glycerol 3-phosphate (G3P) dehydrogenase and fumarate reductase can catalyze under anaerobic conditions the transfer of hydrogens from G3P to fumarate, with attendant generation of high-energy phosphate. The phsophorylation process is more sensitive than the transhydrogenation process to inhibition by the detergent Triton X-100. The same is true with respect to sensitivity to sodium azide, carbonyl cyanide m-chlorophenylhydrazone and N,N'-dicyclohexylcarbodiimide. Such a preparation derived from cells with beta-galactoside permease can accumulate thiomethyl beta-D-galactoside anaerobically, and the accumulation can be stimulated twofold by adding G3P and fumarate. Mutants lacking the membrane-associated Mg2+-dependent adenosine triphosphatase cannot grow anaerobically on glycerol with fumarate as the hydrogen acceptor, although they can grow aerobically on glycerol alone.

Electron transport chain from glycerol 3-phosphate to nitrate in Escherichia coli

It is known that in Escherichia coli two dehydrogenases of the flavoprotein kind can participate in the transfer of hydrogens from sn-glycerol 3-phosphate (G3P) to nitrate and that possession of either enzyme is sufficient to permit anaerobic growth on glycerol as carbon source and nitrate as hydrogen acceptor. Results from this study show that under such a growth condition a protein with light-absorption characteristics of cytochrome b1 is induced. If G3P, nitrate, and adenosine diphosphate are added anaerobically to a particulate fraction prepared from these cells, four reactions can be detected: (i) the reduction of the cytochrome b1-like protein, (ii) the formation of dihydroxyacetone phosphate (DHAP), (iii) the formation of nitrite, and (iv) the generation of adenosine 5'-triphosphate (ATP). The anaerobic G3P dehydrogenase system can yield an ATP-DHAP (or ATP-nitrite) molar ratio of about 0.2, whereas the aerobic G3P dehydrogenase system can yield a corresponding ratio of about 0.3. The hydrogen transfer activity is sensitive to respiratory inhibitors such as cyanide, Rotenone, and 2-heptyl-4-hydroxyquinoline-N-oxide.

Enzyme complex which couples glycerol-3-phosphate dehydrogenation to fumarate reduction in Escherichia coli

Anaerobic growth of Escherichia coli on glycerol as carbon source and fumarate as hydrogen acceptor results in the induction of both anaerobic sn-glycerol-3-phosphate (G3P) dehydrogenase and fumarate reductase. In previous studies, the G3P dehydrogenase was measured by the G3P-dependent reduction of a tetrazolium dye mediated by phenazine methosulfate in the presence of flavine mononucleotide and flavine adenine dinucleotide, and fumarate reductase was measured by the fumarate-dependent oxidation of reduced flavine mononucleotide. Results from the present study indicate that these two enzymes actually constitute a functional complex which is sedimentable at 200,000 x g in 2 h and which can catalyze the dehydrogenation of G3P at the expense of fumarate without any added cofactor. This coupling activity is not constituted by simply mixing an extract containing anaerobic G3P dehydrogenase with another extract containing fumarate reductase. Additional evidence for an organized complex is provided by the high degree of sensitivity of the coupled reaction to low concentrations of the detergents Triton X-100 and Emasol 1130 in comparison with the individual activities of the two component enzymes measured with the aid of artificial cofactors.