A periplasmic arginine transport system that is a member of the ATP-dependent transport superfamily was identified in The gene encoding the periplasmic binding protein () was cloned and the protein overexpressed in LapT was purified to homogeneity using a modified osmotic shock procedure and anion-exchange column chromatography. Filter-binding assays established that LapT is an t-arginine-binding protein. Various amino acids were tested for their ability to inhibit L-arginine binding to LapT. When present in 100-fold excess, only L-arginine, D-arginine and citrulline competed with L-arginine for binding. Arginine transport in whole cells was competitively inhibited by the same amino acids, suggesting that the LapT permease specifically transports L-arginine. The dissociation constant for the L-arginine-LapT complex was 170 nM and the stoichiometry of binding was approximately 0.8 mol L-arginine (mol LapT). A polyclonal antibody raised against the purified protein permitted detection of LapT in periplasmic fractions.


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