Possible Locations for a Common Gene Product in Membrane Transport of Imino-acids and Glycine

Abstract

A GROUP of amino-acids may be suspected of sharing a ‘common’ cellular transport system when an interaction, probably competitive and resulting in inhibition of transport of only members of the group, can be shown in vivo. The evidence for a common system is strengthened when a genetic mutation can be identified, for which the phenotypic manifestation is a disturbance of cellular transport affecting the particular group. In man and other mammals, so-called ‘common’ cellular transport systems have been suggested for the following groups of amino-acids : cystine, lysine, arginine, and ornithine^1–3 ; the dicarboxylic amino-acids⁴ ; proline, hydroxyproline and glycine^5,6. It is interesting that the remainder of the amino-acids normally found in human plasma are affected in the mutant transport phenotype known as Hartnup disease^7,8.