Properties of a Na+-coupled serine-threonine transport system in Escherichia coli.
Based on the following experimental results we conclude that the serine-threonine transport system in Escherichia coli is a Na+-coupled cotransport system. (1) Addition of serine to cell suspensions induced H+ efflux in the presence of Na+. (2) Addition of serine to cell suspensions induced Na+ uptake by cells. (3) Imposition of an artificial electrochemical potential of Na+ in starved cells induced serine uptake. Some of these phenomena were observed when threonine was added instead of serine or inhibited when cells were preincubated with threonine. The Na+/serine (threonine) cotransport system was considerably repressed when cells were grown on a mixture of amino acids. Serine transport in cells grown in the absence of amino acids mixture was stimulated by Na+. The half maximum concentration of Na+ was 21 microM. Sodium ion increased the Vmax of serine transport without affecting the Km.
Hama
H
H
Department of Microbiology, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
Shimamoto
T
T
Tsuda
M
M
Tsuchiya
T
T
D026905:Amino Acid Transport Systems; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D007700:Kinetics; D011522:Protons; D012694:Serine / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013912:Threonine / Q000378:metabolism*
D026905:Amino Acid Transport Systems; D002352:Carrier Proteins; D011522:Protons; D013912:Threonine; D012694:Serine; D012964:Sodium