Kotliar N, Stella C A, Ramos E H
Departamento de Bioquímica, Facultad de Medicina, Universidad de Buenos Aires, Argentina.
Rev Argent Microbiol. 1990 Jan-Mar;22(1):7-16.
L-leucine entrance into Saccharomyces cerevisiae is mediated by the general amino acid permease, GAP and two transport systems, S1 and S2, kinetically characterized. S1 is a high-affinity, low-velocity transport system, operating at lower L-leucine external concentration (0.05-0.1 mM), while S2 is a low-affinity, high-velocity transport system, operating at higher L-leucine external concentration (1.0 mM). In cells grown in minimal medium containing ammonium as sole nitrogen source the values of L-leucine entrance and uptake are smaller than those in cells grown in L-proline containing medium. When GAP is repressed by ammonium, L-leucine entrance is mediate by systems S1 and S2. Both systems are inhibited by ammonium. When GAP is derepressed, in cells grown in L-proline medium, L-leucine is transported by systems S1 and GAP (lower L-leucine external concentration), and mainly by S2 (higher L-leucine external concentration). GAP is the largest system inhibited by ammonium.
L-亮氨酸进入酿酒酵母是由通用氨基酸通透酶GAP以及两个动力学特征明确的转运系统S1和S2介导的。S1是一种高亲和力、低速度的转运系统，在较低的细胞外L-亮氨酸浓度（0.05 - 0.1 mM）下发挥作用，而S2是一种低亲和力、高速度的转运系统，在较高的细胞外L-亮氨酸浓度（1.0 mM）下发挥作用。在以铵作为唯一氮源的基本培养基中生长的细胞中，L-亮氨酸的进入和摄取值低于在含有L-脯氨酸的培养基中生长的细胞。当GAP被铵抑制时，L-亮氨酸的进入由S1和S2系统介导。这两个系统都受到铵的抑制。当GAP去阻遏时，在L-脯氨酸培养基中生长的细胞中，L-亮氨酸在较低的细胞外L-亮氨酸浓度下由S1和GAP系统转运，而在较高的细胞外L-亮氨酸浓度下主要由S2转运。GAP是受铵抑制的最大的系统。
