在虾的肝胰腺中，L-亮氨酸、L-蛋氨酸和 L-苯丙氨酸共用一种 Na(+)/K (+)-依赖性氨基酸转运体。
L-leucine, L-methionine, and L-phenylalanine share a Na(+)/K (+)-dependent amino acid transporter in shrimp hepatopancreas.
机构信息
Department of Biology, 1 UNF Drive, University of North Florida, Jacksonville, FL 32224, USA.
出版信息
J Comp Physiol B. 2013 Aug;183(6):763-71. doi: 10.1007/s00360-013-0758-z. Epub 2013 Apr 25.
Hepatopancreatic brush border membrane vesicles (BBMV), made from Atlantic White shrimp (Litopenaeus setiferus), were used to characterize the transport properties of (3)H-L-leucine influx by these membrane systems and how other essential amino acids and the cations, sodium and potassium, interact with this transport system. (3)H-L-leucine uptake by BBMV was pH-sensitive and occurred against transient transmembrane concentration gradients in both Na(+)- and K(+)-containing incubation media, suggesting that either cation was capable of providing a driving force for amino acid accumulation. (3)H-L-leucine uptake in NaCl or KCl media were each three times greater in acidic pH (pH 5.5) than in alkaline pH (pH 8.5). The essential amino acid, L-methionine, at 20 mM significantly (p < 0.0001) inhibited the 2-min uptakes of 1 mM (3)H-L-leucine in both Na(+)- and K(+)-containing incubation media. The residual (3)H-L-leucine uptake in the two media were significantly greater than zero (p < 0.001), but not significantly different from each other (p > 0.05) and may represent an L-methionine- and cation-independent transport system. (3)H-L-leucine influxes in both NaCl and KCl incubation media were hyperbolic functions of [L-leucine], following the carrier-mediated Michaelis-Menten equation. In NaCl, (3)H-L-leucine influx displayed a low apparent K M (high affinity) and low apparent J max, while in KCl the transport exhibited a high apparent K M (low affinity) and high apparent J max. L-methionine or L-phenylalanine (7 and 20 mM) were competitive inhibitors of (3)H-L-leucine influxes in both NaCl and KCl media, producing a significant (p < 0.01) increase in (3)H-L-leucine influx K M, but no significant response in (3)H-L-leucine influx J max. Potassium was a competitive inhibitor of sodium co-transport with (3)H-L-leucine, significantly (p < 0.01) increasing (3)H-L-leucine influx K M in the presence of sodium, but having negligible effect on (3)H-L-leucine influx J max in the same medium. These results suggest that shrimp BBMV transport (3)H-L-leucine by a single L-methionine- and L-phenylalanine-shared carrier system that is enhanced by acidic pH and can be stimulated by either Na(+) or K(+) acting as co-transport drivers binding to shared activator sites.
肝胰腺刷状缘膜泡（BBMV）由大西洋白虾（Litopenaeus setiferus）制成，用于表征这些膜系统中（3）H-L-亮氨酸流入的转运特性，以及其他必需氨基酸和阳离子（钠和钾）如何与该转运系统相互作用。（3）H-L-亮氨酸在含有 BBVM 的 Na（+）和 K（+）孵育介质中的摄取对 pH 敏感，并在瞬态跨膜浓度梯度下发生，这表明任何阳离子都能够为氨基酸积累提供驱动力。（3）H-L-亮氨酸在 NaCl 或 KCl 介质中的摄取分别在酸性 pH（pH 5.5）下比碱性 pH（pH 8.5）下高 3 倍。在含有 Na（+）和 K（+）的孵育介质中，20 mM 的必需氨基酸 L-蛋氨酸显著（p<0.0001）抑制了 1 mM（3）H-L-亮氨酸的 2 分钟摄取。在两种介质中，剩余的（3）H-L-亮氨酸摄取均显著大于零（p<0.001），但彼此之间没有显著差异（p>0.05），可能代表 L-蛋氨酸和阳离子非依赖性转运系统。（3）H-L-亮氨酸在 NaCl 和 KCl 孵育介质中的流入均为[L-亮氨酸]的双曲线函数，遵循载体介导的米氏方程。在 NaCl 中，（3）H-L-亮氨酸的流入显示出低表观 K M（高亲和力）和低表观 J max，而在 KCl 中，转运表现出高表观 K M（低亲和力）和高表观 J max。L-蛋氨酸或 L-苯丙氨酸（7 和 20 mM）是 NaCl 和 KCl 介质中（3）H-L-亮氨酸流入的竞争性抑制剂，导致（3）H-L-亮氨酸流入 K M 显著（p<0.01）增加，但（3）H-L-亮氨酸流入 J max 无显著变化。钾是与（3）H-L-亮氨酸协同转运的钠离子竞争性抑制剂，在存在钠离子的情况下，显著（p<0.01）增加（3）H-L-亮氨酸流入 K M，但对同一介质中（3）H-L-亮氨酸流入 J max 几乎没有影响。这些结果表明，虾 BBMV 通过单一的 L-蛋氨酸和 L-苯丙氨酸共享载体系统转运（3）H-L-亮氨酸，该系统受酸性 pH 增强，并可被 Na（+）或 K（+）刺激，Na（+）或 K（+）作为协同转运驱动剂与共享激活位点结合。
Zotero 插件