Kotliar N, Stella C A, Ramos E H, Mattoon J R
Department of Biology, University of Colorado, Colorado Springs 80933-7150.
Cell Mol Biol (Noisy-le-grand). 1994 Sep;40(6):833-42.
L-leucine uptake in Saccharomyces cerevisiae is mediated by three different transport systems, S1, S2 and GAP1. Their activities are dependent on the nitrogen source of the culture media. Wild type cells grown in L-proline exhibit a single transport system with high affinity and high Vmax that is partially inhibited by L-citrulline. A gap1 mutant shows two transport systems with Km and Vmax values similar to those previously described as S1 and S2, this transport activity is not inhibited by D-leucine, D-isoleucine or D-valine. Two systems can be also determined in wild type cells grown in rich medium containing a mixed nitrogen source where decreased GAP1 function is observed. In either wild type or gap1 cells grown in medium containing ammonium ions as sole nitrogen source, L-leucine uptake kinetics shows two systems with lower Vmax and similar Km values to those of the S1 and S2 systems. These results show that in S. cerevisiae GAP1, S1 and S2 participate in L-leucine entrance in cells grown in a poor nitrogen source, and that S1 and S2 are two ammonia-sensitive permeases that mediate the uptake in cells grown in a rich nitrogen source.
酿酒酵母中L-亮氨酸的摄取由三种不同的转运系统S1、S2和GAP1介导。它们的活性取决于培养基的氮源。在L-脯氨酸中生长的野生型细胞表现出一种具有高亲和力和高Vmax的单一转运系统，该系统会被L-瓜氨酸部分抑制。gap1突变体显示出两种转运系统，其Km和Vmax值与先前描述的S1和S2相似，这种转运活性不受D-亮氨酸、D-异亮氨酸或D-缬氨酸的抑制。在含有混合氮源的丰富培养基中生长的野生型细胞中也可以确定两种系统，在这些细胞中观察到GAP1功能降低。在以铵离子作为唯一氮源的培养基中生长的野生型或gap1细胞中，L-亮氨酸摄取动力学显示出两种系统，其Vmax较低，Km值与S1和S2系统相似。这些结果表明，在酿酒酵母中，GAP1、S1和S2参与了在贫氮源中生长的细胞中L-亮氨酸的进入，并且S1和S2是两种氨敏感的通透酶，介导在富氮源中生长的细胞中的摄取。
