PROPERTIES OF A NA+ GALACTOSE(GLUCOSE) SYMPORT SYSTEM IN VIBRIO-PARAHAEMOLYTICUS/

We have investigated galactose transport in a mutant strain of Vibrio parahaemolyticus that lacks a glucose-PTS (phosphoenolpyruvate:carbohy drate phosphotransferase system) and a trehalose-PTS. Cells of the V. parahaemolyticus actively transported D-galactose and Na+ greatly stim ulated the transport, Maximum stimulation of D-galactose transport act ivity was observed at 10 mM NaCl, and Na+ could be replaced with Li+. Addition of galactose to the cell suspension under anaerobic condition s elicited Na+ uptake. Therefore, we conclude that this organism accom plishes galactose transport by a Na+/solute symport mechanism. Judging from inhibition results, D-galactose, D-glucose and to a lesser exten t alpha-D-fucose are substrates of this transport system. The Na+/gala ctose symport system exhibited a high affinity for D-galactose (K-m: 4 0 mu M) and showed a relatively lower affinity for D-glucose (K-m: 420 mu M), but the maximum velocities for galactose and glucose transport were almost same (about 52 nmol/min per mg protein). The Na+/D-galact ose symport system was induced by either D-galactose or alpha-D-fucose , and repressed by D-glucose.