Escherichia coli alpha-ketoglutarate permease is a constitutively expressed proton symporter.

Escherichia coli kgtP which maps at 56.5 min codes for alpha-ketoglutarate permease (KgtP). This protein, expressed from the cloned gene using the T7 polymerase system and 35S]methionine labeling, fractionated with cell membranes. Right-side-out (RSO) membrane vesicles prepared from a kgtP negative mutant strain did not transport alpha-ketoglutarate, but RSO vesicles from the same strain expressing KgtP from a transforming plasmid transported alpha-ketoglutarate effectively as measured by uptake of the 14C-labeled substrate. E. coli JC7623 strain grown in M9 minimal medium with glucose, glycerol, or alpha-ketoglutarate as carbon source contained a 1.3-kilobase RNA which hybridized to nick-translated kgtP probe. In addition, strain MC1061 cultures grown under these same conditions were all capable of transporting alpha-ketoglutarate, demonstrating that KgtP is constitutively expressed. The Km and Vmax of KgtP assayed in strain MC1061 vesicles were 13-46 microM and 8 nmol/min/mg protein, respectively. Uncouplers that permeabilized the membrane to protons inhibited alpha-ketoglutarate transport into energized vesicles, and the addition of alpha-ketoglutarate to vesicle suspensions under non-energized conditions resulted in an increase in pH. These results indicate that KgtP is an alpha-ketoglutarate-proton symporter.