Palacin M, Fernández E, Chillarón J, Zorzano A
Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona i Parc Cientific de Barcelona, Spain.
Mol Membr Biol. 2001 Jan-Mar;18(1):21-6.
Amino acid transport in mammalian plasma membranes is mediated by a multiplicity of amino acid transport systems. Some of them (systems L, y+ L, x(c)- and b(o,+)) are the result of the activity of heteromeric amino acid transporters (HAT) (i.e. transport activity is elicited by the coexpression of a heavy and a light subunit). The two heavy subunits known today (HSHAT: rBAT and 4F2hc) were identified in 1992, and light subunits (LSHAT: LAT-1, LAT-2, asc-1, y+ LAT-1, y+ LAT-2, xCT and b(o,+)AT) have been cloned in the last 2 years. Defects in two genes of this family (SLC3A1, encoding rBAT and SLC7A9, encoding b(o,+)AT) are responsible for cystinuria, an inherited aminoaciduria of cystine and dibasic amino acids. This finding and functional studies of rBAT and b(o,+)AT suggested that these two proteins encompassed the high-affinity renal reabsorption system of cystine. In contrast to this view, immunofluorescence studies showed that rBAT is most abundant in the proximal straight tubule, and b(o,+)AT is most abundant in the proximal convoluted tubule of the nephron. The need for a new light subunit for rBAT and a heavy subunit for b(o,+)AT is discussed.
哺乳动物质膜中的氨基酸转运由多种氨基酸转运系统介导。其中一些系统（L、y+L、x(c)-和b(o,+)）是异源氨基酸转运体（HAT）活性的结果（即转运活性由重亚基和轻亚基的共表达引发）。如今已知的两个重亚基（HSHAT：rBAT和4F2hc）于1992年被鉴定出来，而轻亚基（LSHAT：LAT-1、LAT-2、asc-1、y+LAT-1、y+LAT-2、xCT和b(o,+)AT）在过去两年中已被克隆。该家族的两个基因（编码rBAT的SLC3A1和编码b(o,+)AT的SLC7A9）存在缺陷是导致胱氨酸尿症的原因，胱氨酸尿症是一种遗传性的胱氨酸和二碱基氨基酸尿症。这一发现以及对rBAT和b(o,+)AT的功能研究表明，这两种蛋白质包含了胱氨酸的高亲和力肾重吸收系统。与这一观点相反，免疫荧光研究表明，rBAT在近端直小管中最为丰富，而b(o,+)AT在肾单位的近端曲小管中最为丰富。文中讨论了rBAT需要一种新的轻亚基以及b(o,+)AT需要一种新的重亚基的问题。
