STRUCTURAL REQUIREMENTS FOR AMINO ACID INHIBITION OF Na+‐DEPENDENT PROLINE UPTAKE BY RAT BRAIN SYNAPTOSOMES

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Abstract
Abstract— The structural requirements for amino acid inhibition of Na+‐dependent proline uptake by rat brain synaptosomal fractions were investigated. It is shown that the amino group has to be in the α‐position to strongly inhibit proline uptake. Hydroxyamino acids are less potent inhibitors than the parent amino acids. Amino acids with net positive or negative charges on their molecules exert no effect, whereas elimination of the net charge results in compounds with profound inhibitory effects. Blocking of the carboxyl group reduces the inhibition, but does not abolish it. Since acetylation of the α‐amino group results in elimination of the inhibitory effect whereas N‐methylation does not, it is concluded that in the interaction of an amino acid with the proline transport site the positive charge on the amino group plays the most critical role.