In the context of transport systems, three main groups of amino acids may be recognized: anionic, cationic and neutral. Cellular protein synthesis and other metabolic processes demand uninterrupted delivery of all amino acids at appropriate sites. The study of amino acid transport and associated systems is thus of critical importance, for example, to those interested in the processes of intestinal absorption and brain function. Animals have a wide array of cells and this diversity is matched by a complex system of transporters of amino acids which operates on the basis of substrate specificity and ion requirements (Matthews, 2000). Thus, glutamate movement in the central nervous system is mediated via distinct Na-dependent proteins of the excitatory amino acid transport (EAAT) class. Five such transporters (EAAT 1-5) have been cloned from mammalian tissue and their modulation by other proteins is the subject of
© CAB International 2003. Amino Acids in Animal Nutrition, 2nd edition (ed. J.P.F. D'Mello)
continuing studies (Jackson et ai, 2001). It is important to recognize, however, that amino acids in different classes may share the same transport system. Thus, three transport systems recognize both lysine and leucine. Details of the biochemical and molecular characterization of the various transport systems for the major classes of amino acids are presented in Chapter 3.
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