Fincham D A, Ellory J C, Young J D
School of Applied Sciences, Wolverhampton Polytechnic, United Kingdom.
Can J Physiol Pharmacol. 1992 Aug;70(8):1117-27. doi: 10.1139/y92-155.
In thoroughbred horses, red blood cell amino acid transport activity is Na(+)-independent and controlled by three codominant genetic alleles (h, l, s), coding for high-affinity system asc1 (L-alanine apparent Km for influx at 37 degrees C congruent to 0.35 mM), low-affinity system asc2 (L-alanine Km congruent to 14 mM), and transport deficiency, respectively. The present study investigated amino acid transport mechanisms in red cells from four wild species: Przewalski's horse (Equus przewalskii), Hartmann's zebra (Zebra hartmannae), Grevy's zebra (Zebra grevyi), and onager (Equus hemonius). Red blood cell samples from different Przewalski's horses exhibited uniformly high rates of L-alanine uptake, mediated by a high-affinity asc1-type transport system. Mean apparent Km and Vmax values (+/- SE) for L-alanine influx at 37 degrees C in red cells from 10 individual animals were 0.373 +/- 0.068 mM and 2.27 +/- 0.11 mmol (L cells.h), respectively. As in thoroughbreds, the Przewalski's horse transporter interacted with dibasic as well as neutral amino acids. However, the Przewalski asc1 isoform transported L-lysine with a substantially (6.4-fold) higher apparent affinity than its thoroughbred counterpart (Km for influx 1.4 mM at 37 degrees C) and was also less prone to trans-stimulation effects. The novel high apparent affinity of the Przewalski's horse transporter for L-lysine provides additional key evidence of functional and possible structural similarities between asc and the classical Na(+)-dependent system ASC and between these systems and the Na(+)-independent dibasic amino acid transport system y+. Unlike Przewalski's horse, zebra red cells were polymorphic with respect to L-alanine transport activity, showing high-affinity or low-affinity saturable mechanisms of L-alanine uptake. Onager red cells transported this amino acid with intermediate affinity (apparent Km for influx 3.0 mM at 37 degrees C). Radiation inactivation analysis was used to estimate the target size of system asc in red cells from Przewalski's horse. The transporter's in situ apparent molecular weight was 158,000 +/- 2500 (SE).
在纯种马中，红细胞氨基酸转运活性不依赖于Na(+)，并受三个共显性遗传等位基因（h、l、s）控制，它们分别编码高亲和力的asc1系统（37℃时L-丙氨酸流入的表观Km约为0.35 mM）、低亲和力的asc2系统（L-丙氨酸Km约为14 mM）和转运缺陷。本研究调查了四种野生物种红细胞中的氨基酸转运机制：普氏野马（Equus przewalskii）、哈特曼斑马（Zebra hartmannae）、细纹斑马（Zebra grevyi）和中亚野驴（Equus hemonius）。来自不同普氏野马的红细胞样本表现出一致的高L-丙氨酸摄取率，这是由高亲和力的asc1型转运系统介导的。10只个体动物红细胞在37℃时L-丙氨酸流入的平均表观Km和Vmax值（±SE）分别为0.373±0.068 mM和2.27±0.11 mmol/（L细胞·h）。与纯种马一样，普氏野马的转运体与二价氨基酸以及中性氨基酸相互作用。然而，普氏野马的asc1亚型转运L-赖氨酸的表观亲和力比纯种马的对应物高得多（6.4倍）（37℃时流入的Km为1.4 mM），并且也不太容易受到反式刺激效应的影响。普氏野马转运体对L-赖氨酸的新的高表观亲和力提供了额外的关键证据，证明asc与经典的Na(+)依赖性系统ASC之间以及这些系统与Na(+)非依赖性二价氨基酸转运系统y+之间在功能和可能的结构上存在相似性。与普氏野马不同，斑马红细胞在L-丙氨酸转运活性方面具有多态性，表现出L-丙氨酸摄取的高亲和力或低亲和力饱和机制。中亚野驴红细胞以中等亲和力转运这种氨基酸（37℃时流入的表观Km为3.0 mM）。采用辐射失活分析来估计普氏野马红细胞中asc系统的靶标大小。转运体的原位表观分子量为158,000±2500（SE）。
