Circumstantial Evidence for Cytochromeb1Involvement in the Functioning of lac-Permease in RespiringEscherichia coli

Abstract The structure of the haem-binding site of cytochrome b 1 and particularly the fact that the two protein ligands of the haem are methionines could explain a correlation found between loss of lac-permease activity and replacement of methionine by norleucine in the protein of aerobically respiring E. coli . If cytochrome b 1 is essential for lac-permease mediated transport in whole bacteria as this correlation suggests, translocation of substrate by this permease must be coupled to electron transport. Such a dependence would invalidate the chemiosmotic interpretation of lactose transport in E. coli in its present form and would be in variance with the coupling-by-energy theories of lactose transport that exempted translocation from dependence on energy yielding processes.