Multiple transport systems for basic amino acid transport in streptomyces hydrogenans

Abstract

In Streptomyces hydrogenans the uptake of basic amino acids occurs via several transport systems: 1. 1. One system (System b Arg) is highly specific for arginine ( K m = 7.10−6 M). l-Arginine influx is only inhibited by closely related analogs such as d-arginine, canavanine and arginine methyl ester, but not by lysine, ornithine, neutral and acidic amino acids. 2. 2. A second system (System b Arg/Lys) transports both arginine ( K m = 0.6 · 10−6 M) and lysine ( K m = 0.9·10−6 M). This system has a higher affinity for l-arginine than System b Arg. Cells grown in synthetic media containing 12 mM l-lysine or l-arginine show a much higher transport capacity than cells grown in complete media or synthetic media with NH 4Cl as nitrogen donor. These differences in transport capacity strongly support the multi-component concept of basic amino acid transport in Streptomyces cells. System b Arg/Lys can be inhibited by analogs of arginine and lysine but not by neutral and acidic amino acids. 3. 3. At very high extracellular concentrations of lysine or arginine both amino acids are transported via a system primarily mediating the uptake of neutral amino acids (System n). The capacity of this system is high but its affinity to basic amino acids is very low [ K m (arginine) = 0.7·10−3 M; K m (lysine) = 1.6·10−3 M]. This system shows exchange between neutral and basic amino acids.