Properties of a Na+/galactose(glucose) symport system in Vibrio parahaemolyticus

摘要

We have investigated galactose transport in a mutant strain of Vibrio parahaemolyticus that lacks a glucose-PTS (phosphoenolpyruvate: carbohydrate phosphotransferase system) and a trehalose-PTS. Cells of the V. parahaemolyticus actively transported -galactose and Na+ greatly stimulated the transport. Maximum stimulation of -galactose transport activity was observed at 10 mM NaCl, and Na+ could be replaced with Li+. Addition of galactose to the cell suspension under anaerobic conditions elicited Na+ uptake. Therefore, we conclude that this organism accomplishes galactose transport by a Na+/solute symport mechanism. Judging from inhibition results, -galactose, -glucose and to a lesser extent α--fucose are substrates of this transport system. The Na+/galactose symport system exhibited a high affinity for -galactose (Km: 40 μM)and showed a relatively lower affinity for -glucose (Km: 420 μM), but the maximum velocities for galactose and glucose transport were almost same (about 52 nmol/min per mg protein). The Na+/-galactose symport system was induced by either -galactose or α--fucose, and repressed by -glucose.