The amino acid transport system b(o,+) and cystinuria.
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.
Palacin
M
M
Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona i Parc Cientific de Barcelona, Spain. mpalacin@porthos.bio.ub.es
Fernández
E
E
Chillarón
J
J
Zorzano
A
A
D026905:Amino Acid Transport Systems / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003553:Cystine / Q000378:metabolism; D003555:Cystinuria / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008954:Models, Biological
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D003553:Cystine