Active transport of proline by Coxiella burnetii

The obligate intracellular rickettsia, Coxiella burnetii, was shown to possess an energy dependent proline transport system which displayed a high degree of specificity and was highly dependent on pH. Transport was maximal at pH 3.0 to 4.5, a pH range approximately that of the host cell phagolysosome where the agent replicates. Transport was inhibited by the uncouplers carbonyl cyanide m-chlorophenylhydrazone and dinitrophenol, but not by sodium arsenite. In the presence of glutamate, a preferred energy source, proline uptake was enhanced more than two-fold. This enhancement of proline uptake was greatly decreased in the presence of sodium arsenite. The addition of glutamate decreased the apparent Km for proline transport from 45 microM to 15 microM, with the Vmax increasing from 3.6 pmol s-1 (mg dry wt)-1 to 4.8 pmol s-1 (mg dry wt)-1. Two proline analogues, furoic acid and azetidine-2-carboxylic acid, were effective inhibitors of proline transport. D-Proline, 4-hydroxyproline, glycine and proline amide inhibited transport minimally, while no inhibition was seen with succinate, pyruvate or glutamate.