Location of the Catalytic Site of the Respiratory Fumarate Reductase of Escherichia coli

SUMMARY: The location of the catalytic site of the membrane-bound respiratory fumarate reductase of Escherichia coli was investigated using mutants and inhibitors of dicarboxylic acid transport. Comparison of apparent K_m and V_max values for fumarate in intact cells and in inverted membrane vesicles showed that externally added fumarate was required to be transported across the cytoplasmic membrane prior to reduction. The catalytic site of fumarate reductase must therefore be located on the cytoplasmic face of the membrane.