THE HUMAN BIOCHEMICAL GENETICS OF AMINO ACID TRANSPORT

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Abstract
What is the relevance of these investigations when so many other problems in medicine seem to claim priority? First of all, these studies are one of several approaches toward an understanding of the plasma membrane, which is an essential cellular component, but whose physical and chemical characteristics are poorly understood. Research into the human biochemical genetics of amino acid transport has led us to believe that many gene loci control a wide spectrum of specific membrane proteins which act as sites where amino acids migrate across cell membranes; this is a valuable concept in its own right, and it is in keeping with much other work on the nature of membrane transport processes. At first it seemed redundant that more than one site should serve the transport of a single amino acid. Yet, this is apparently a long-standing adaptation of cellular membranes. Microorganisms face their environment armed with membranes adapted to absorb solutes in one way at low concentrations and in another at high concentrations. Kepes has described the obvious advantages which such constitutive functions might have for the economy of an organism which may have to adapt to a nutritional environment fluctuating between dearth and abundance. See image in the PDF file Retention of complex membrane systems in metazoan species stabilizes the commerce of intermediate metabolism and contributes to the equilibrium between the cell and its environment; without this equilibrium, perhaps we would not recognize perturbation so readily, and some forms of disease, such as can be detected by the screening tests now in vogue, would go unrecognized. Without mediated transport, human malnutrition would be a worse scourge than it is, because tissues which can transport efficiently against a chemical gradient will accumulate as much nourishment as possible from the environment, even in famine. But, there is another reason to study membrane transport. We hope the time will come when we know enough to design molecules for therapeutic purposes, to "fit" different transport sites, and to direct their traffic into particular tissues or to probe particular functions. If this should happen, then genetics, biochemistry, pharmacology, and many of the other disciplines would be united in one enterprise for the benefit of the patient.

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