Bröer Stefan
School of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, ACT 0200 Canberra, Australia.
Pflugers Arch. 2002 Jul;444(4):457-66. doi: 10.1007/s00424-002-0840-y. Epub 2002 Apr 23.
The molecular identification of almost all physiologically characterized amino acid transporters in recent years has facilitated the functional analysis of this important class of transport proteins. The picture that emerges from these studies is that antiport is the prevalent mode of amino acid transport rather than a combination of uniporters and cotransporters. Mainly neurotransmitters and osmolytes are transported by complex cotransport mechanisms that allow a high intracellular accumulation. Antiport mechanisms almost invariably include the nonessential amino acids alanine and glutamine, which are used as exchange substrates. The intracellular level of both amino acids is well regulated by Na(+)/amino acid cotransporters. Transport mechanisms are not conserved within families and may change with mutation of even a single amino acid residue in the transport protein. Thus transport mechanisms are easily adapted to physiological demands during evolution.
近年来，几乎所有经生理学特征鉴定的氨基酸转运蛋白的分子鉴定都推动了对这一重要转运蛋白类别的功能分析。这些研究呈现出的情况是，反向转运是氨基酸转运的普遍模式，而非单向转运体和协同转运体的组合。主要是神经递质和渗透溶质通过复杂的协同转运机制进行转运，从而实现细胞内的高浓度积累。反向转运机制几乎总是包括非必需氨基酸丙氨酸和谷氨酰胺，它们用作交换底物。这两种氨基酸的细胞内水平都受到钠/氨基酸协同转运体的良好调节。转运机制在不同家族中并不保守，甚至转运蛋白中单个氨基酸残基的突变都可能导致其改变。因此，在进化过程中，转运机制很容易适应生理需求。
