DeBusk R M, DeBusk A G
J Bacteriol. 1980 Jul;143(1):188-97. doi: 10.1128/jb.143.1.188-197.1980.
The fundamental properties of the general amino acid transport system of Neurospora crassa were investigated in the conidial stage of the life cycle. The transport activity was found to be under genetic control, and an isogenic set of mutants deficient for the neutral, basic, or general amino acid transport systems and combinations thereof was constructed and used for analyzing the properties specific to the general permease. Amino acid transport by this system was found to be a carrier-mediated active process with broad specificity for the neutral and basic amino acids. Kinetic analysis revealed that a common binding site functioned to transport both neutral and basic amino acids and that the permease had a high affinity for its substrates. The kinetic parameters Km, Vmax, and Ki were defined for several substrates. Two modes of regulation were detected: substrate inhibition and ammonium repression. Activity of the general system was enhanced by the removal of ammonium ions from the incubation medium with a concomitant decline in either neutral or basic permease activity, suggesting that a common component exists between the neutral and the general systems and between the basic and the general systems.
在粗糙脉孢菌生命周期的分生孢子阶段，对其通用氨基酸转运系统的基本特性进行了研究。发现转运活性受遗传控制，并构建了一组同基因的突变体，这些突变体缺乏中性、碱性或通用氨基酸转运系统及其组合，并用于分析通用通透酶的特异性特性。该系统的氨基酸转运是一种载体介导的主动过程，对中性和碱性氨基酸具有广泛的特异性。动力学分析表明，一个共同的结合位点负责转运中性和碱性氨基酸，并且通透酶对其底物具有高亲和力。为几种底物定义了动力学参数Km、Vmax和Ki。检测到两种调节模式：底物抑制和铵阻遏。通过从孵育培养基中去除铵离子，通用系统的活性增强，同时中性或碱性通透酶活性下降，这表明中性和通用系统之间以及碱性和通用系统之间存在共同成分。
