Amino Acid Transport in Mycobacterium smegmatis

Abstract

The transport of D-alanine, D-glutamic acid, and D-valine in Mycobacterium smegmatis was compared quantitatively with that of their L-isomers. It appeared that the uptake of D-alanine was mediated by an active process displaying saturation kinetics characteristic of enzyme function, whereas the uptake of D-glutamic acid was accomplished by a passive process showing diffusion kinetics. Both processes were involved in the uptake of L-alanine, L-glutamic acid, D-valine, and L-valine. D-Valine competed with L-valine for entry into the cell through a single active process. D-Alanine and L-alanine also utilized the same active process, but the D-isomer could not enter the cell through the passive process. The passive process exhibited characteristics of diffusion, but was sensitive to sulfhydryl-blocking reagents and showed competition among structurally related amino acids. These last findings suggested that the passive process is a facilitated diffusion.

Resistance to d-Cycloserine in the Tubercle Bacilli: Mutation Rate and Transport of Alanine in Parental Cells and Drug-Resistant Mutants

“…on September 6, 2020 by guest http://aem.asm.org/ Downloaded from that the alanine-permease system is inducible in these bacteria (2) and is in agreement with Yabu's investigations in M. smegmatis (10). Pulse experiments indicated that neither drug interferes with the subsequent induction of the permease system by L-alanine (Table 1); it was also observed that exposing the cells to the drugs during the whole period of induction did not interfere with the induction process.…”

Uptake and Utilization of Glutamic Acid by Cryptococcus albidus

“…The uptake of L-glutamic acid by C. albidus showed a break in the saturation curve at high amino acid concentrations. Such nonlinear, double reciprocal plots have been found in many bacteria, e.g., Salmonella typhimurium (2), Escherichia coli (17), Pseudomonas aeruginosa (20), Mycobacterium smegmatis (32), Streptococcus faecalis (31) and Streptomyces hydrogenans (13). In general, a particular amino acid was transported by two distinct transport systems: one had a high affinity (Ki) and was very specific for the particular amino acid, whereas the second system had a lower affinity for the amino acid (Ki) and was relatively nonspecific in that it also transported related amino acids (2,7,13,20).…”

Comparative Physiological Studies of the Yeast and Mycelial Forms of Histoplasma capsulatum : Uptake and Incorporation of l -Leucine

“…The complex nature of the L-leucine uptake process in both morphological forms of H. capsulatum is indicated by the break in saturation curves at high amino acid concentrations. It was reported that nonlinear, double-reciprocal plots are characteristic of many amino acid transport systems in Pseudomonas aeruginosa (14), and such nonlinearity was discovered in other bacteria and yeasts (3,8,10,11,30). In general, these reports point out that a particular amino acid is transported by two different carrier sites: one has a high affinity (Kmn) and is completely specific for the amino acid, and the other is nonspecific with a low affinity (Kin).…”

“…The Km values for the transport system operative at higher external amino acid concentration was theoretically infinite, because the second phase of the double-reciprocal plot passed almost through the origin, indicating that L-leucine was entering the cell by simple diffusion. If a process other than simple diffusion were operative, a second but finite value of the Km should have been observed (3,8,10,30).…”