Kiritani K, Ohnishi K
J Bacteriol. 1977 Feb;129(2):589-98. doi: 10.1128/jb.129.2.589-598.1977.
Kinetics of the transport systems common for entry of L-isoleucine, L-leucine, and L-valine in Salmonella typhimurium LT2 have been analyzed as a function of substrateconcentration in the range of 0.5 to 45 muM. The systems of transport mutants, KA203 (ilvT3) and KA204 (ilvT4), are composed of two components; apparent Km values for uptake of isoleucine, leucine, and valine by the low Km component are 2 muM, 2 to 3 muM, and 1 muM, respectively, and by the high Km component 30 muM, 20 to 40 muM, and 0.1 mM, respectively. The transport system(s) of the wild type has not been separated into components but rather displays single Km values of 9 muM for isoleucine, 10 muM for leucine, and 30 muM for valine. The transport activity of the wild type was repressed by L-leucine, alpha ketoisocaproate, glycyl-L-isoleucine, glycyl-L-leucine, and glycyl-L-methionine. That for the transport mutants was repressed by L-alanine, L-isoleucine, L-methionine, L-valine, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, glycyl-L-alanine, glycyl-L-threonine, and glycyl-L-valine, in addition to the compounds described above. Repression of the mutant transport systems resulted in disappearance of the low Km component for valine uptake, together with a decrease in Vmax of the high Km component; the kinetic analysis with isoleucine and leucine as substrates was not possible because of poor uptake. The maximum reduction of the transport activity for isoleucine was obtained after growing cells for two to three generations in a medium supplemented with repressor, and for the depression, protein synthesis was essential after removal of the repressor. The transport activity for labeled isoleucine in the transport mutant and wild-type strains was inhibited by unlabeled L-alanine, L-cysteine, L-isoleucine, L-leucine, L-methionine, L-threonine, and L-valine. D-Amino acids neither repressed nor inhibited the transport activity of cells for entry of isoleucine.
鼠伤寒沙门氏菌LT2中L-异亮氨酸、L-亮氨酸和L-缬氨酸进入细胞所共有的转运系统的动力学，已作为底物浓度在0.5至45μM范围内的函数进行了分析。转运突变体KA203（ilvT3）和KA204（ilvT4）的系统由两个组分组成；低Km组分摄取异亮氨酸、亮氨酸和缬氨酸的表观Km值分别为2μM、2至3μM和1μM，高Km组分的分别为30μM、20至40μM和0.1mM。野生型的转运系统尚未分离成组分，而是显示异亮氨酸的单一Km值为9μM，亮氨酸为10μM，缬氨酸为30μM。野生型的转运活性受到L-亮氨酸、α-酮异己酸、甘氨酰-L-异亮氨酸、甘氨酰-L-亮氨酸和甘氨酰-L-甲硫氨酸的抑制。转运突变体的转运活性除了受到上述化合物的抑制外，还受到L-丙氨酸、L-异亮氨酸、L-甲硫氨酸、L-缬氨酸、α-酮异戊酸、α-酮-β-甲基戊酸、甘氨酰-L-丙氨酸、甘氨酰-L-苏氨酸和甘氨酰-L-缬氨酸的抑制。突变体转运系统的抑制导致缬氨酸摄取的低Km组分消失，同时高Km组分的Vmax降低；由于摄取不佳，无法以异亮氨酸和亮氨酸作为底物进行动力学分析。在添加了阻遏物的培养基中培养细胞两到三代后，异亮氨酸转运活性得到最大程度的降低，而对于阻遏作用，去除阻遏物后蛋白质合成至关重要。转运突变体和野生型菌株中标记异亮氨酸的转运活性受到未标记的L-丙氨酸、L-半胱氨酸、L-异亮氨酸、L-亮氨酸、L-甲硫氨酸、L-苏氨酸和L-缬氨酸的抑制。D-氨基酸既不抑制也不抑制细胞摄取异亮氨酸的转运活性。
