The characterization and affinity labeling of the L-tryrosineL-phenylalanine transport system of Bacillus subtilis

Abstract

This dissertation describes the kinetics, specificity, mechanisms, and affinity labeling of the L-tyrosine/L-phenylalanine transport system in whole cells of Bacillus subtilis. The L-tyrosine/L-phenylalanine transport system was inhibited by amino acid analogs that: (i), possessed an aromatic side chain; and (ii), possessed a positively charged amino group. Modification of the carboxyl group of either L0tyrosine or L-phenylalanine did not appreciably affect their binding. Other amino acids, such as, L-leucine and L-aspartate noncompetitively inhibited L-tyrosine/L-phenylalanine uptake. A significant portion of L-tyrosine or L-phenylalanine transported appeared to be sequestered inside the cells since it was not lost by dilution of the external medium or by addition of energy poisons. The other portion of these amino acids in the pool was subject to exchange, dilution, and loss induced by energy poisons. Cyanide and azide, inhibitors of the electron transport chain, inhibited the uptake of L-tyrosine and L-phenylalanine into whole cells. Sulfhydryl reagents irreversibly inhibited L-tyrosine/L-phenylalanine transport.