Li Z C, Bush D R
Photosynthesis Research Unit. U.S. Department of Agriculture, Agricultural Research Service, University of Illinois, Urbana, Illinois 61801.
Plant Physiol. 1990 Sep;94(1):268-77. doi: 10.1104/pp.94.1.268.
Amino acid transport into plasma membrane vesicles isolated from mature sugar beet (Beta vulgaris L. cv Great Western) leaves was investigated. The transport of alanine, leucine, glutamine, glutamate, isoleucine, and arginine was driven by a trans-membrane proton concentration difference. DeltapH-Dependent alanine, leucine, glutamine, and glutamate transport exhibited simple Michaelis-Menten kinetics, and double-reciprocal plots of the data were linear with apparent K(m) values of 272, 346, 258, and 1981 micromolar, respectively. These results are consistent with carrier mediated transport. DeltapH-Dependent isoleucine and arginine transport exhibited biphasic kinetics, suggesting these amino acids may be transported by at least two transport systems. Symport mediated alanine transport was electrogenic as demonstrated by the effect of membrane potential (DeltaPsi) on DeltapH-dependent flux. In the absence of significant charge compensation, a low rate of alanine transport was observed. When DeltaPsi was held at 0 millivolt with symmetric potassium concentrations and valinomycin, the rate of flux was stimulated fourfold. In the presence of a negative DeltaPsi, alanine transport increased sixfold. These results are consistent with an electrogenic transport process which results in a net flux of positive charge into the vesicles. The effect of changing DeltaPsi on the kinetics of alanine transport altered V(max) with no apparent change in K(m). Amino acid transport was inhibited by the protein modifier diethyl pyrocarbonate, but was insensitive to N-ethylmaleimide, 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid, p-chloromercuribenzenesulfonic acid, phenylglyoxal, and N,N'-dicyclohexylcarbodiimide. Four amino acid symport systems, two neutral, one acidic, and one basic, were resolved based on inter-amino acid competition experiments. One neutral system appears to be active for all neutral amino acids while the second exhibited a low affinity for isoleucine, threonine, valine, and proline. Although each symport was relatively specific for a given group of amino acids, each system exhibited some crossover specificity for amino acids in other groups.
对从成熟甜菜（Beta vulgaris L. cv Great Western）叶片中分离出的质膜囊泡中的氨基酸转运进行了研究。丙氨酸、亮氨酸、谷氨酰胺、谷氨酸、异亮氨酸和精氨酸的转运由跨膜质子浓度差驱动。依赖ΔpH的丙氨酸、亮氨酸、谷氨酰胺和谷氨酸转运表现出简单的米氏动力学，数据的双倒数图呈线性，表观K(m)值分别为272、346、258和1981微摩尔。这些结果与载体介导的转运一致。依赖ΔpH的异亮氨酸和精氨酸转运表现出双相动力学，表明这些氨基酸可能由至少两种转运系统转运。如膜电位（ΔΨ）对依赖ΔpH的通量的影响所示，同向转运介导的丙氨酸转运是生电的。在没有显著电荷补偿的情况下，观察到丙氨酸转运速率较低。当用对称的钾浓度和缬氨霉素将ΔΨ维持在0毫伏时，通量速率增加了四倍。在存在负ΔΨ的情况下，丙氨酸转运增加了六倍。这些结果与一种生电转运过程一致，该过程导致正电荷净流入囊泡。改变ΔΨ对丙氨酸转运动力学的影响改变了V(max)，而K(m)没有明显变化。氨基酸转运受到蛋白质修饰剂焦碳酸二乙酯的抑制，但对N-乙基马来酰亚胺、4,4'-二异硫氰酸-2,2'-二苯乙烯二磺酸、对氯汞苯磺酸、苯乙二醛和N,N'-二环己基碳二亚胺不敏感。基于氨基酸间竞争实验解析出四个氨基酸同向转运系统，两个中性的、一个酸性的和一个碱性的。一个中性系统似乎对所有中性氨基酸都有活性，而第二个对异亮氨酸、苏氨酸、缬氨酸和脯氨酸表现出低亲和力。尽管每个同向转运对给定的一组氨基酸相对特异，但每个系统对其他组中的氨基酸也表现出一些交叉特异性。
