Some characteristics of the uptake of glutamine by corn scutellum.
Slices of corn scutellum were used to study amino acid uptake, a natural function of this tissue. The uptake of glutamine was found to be inhibited by several monovalent cations. The accompanying anion did not affect the inhibition. Divalent cations stimulated glutamine uptake, particularly at high glutamine concentrations. The inhibition by monovalent cations was reversed by divalent cations.There was a broad pH optimum (4.3-5.2), and a wide range of pH values over which substantial rates of glutamine uptake were observed (3-7).Seventeen protein amino acids were tested for their effects on glutamine uptake. l-Alanine, l-cysteine, l-glutamic acid, glycine, l-serine, and l-methionine were the only inhibitory amino acids. The inhibition by alanine and methionine was overcome at high glutamine concentrations whereas the inhibition by monovalent cations was not. The inhibition by amino acids was not reversed by divalent cations. d-Alanine and d-methionine had no effect on glutamine uptake.High concentrations of sucrose (0.5 m) did not affect glutamine uptake. Thus, osmotic shock did not cause a dissociation of a transport protein from a membrane. Mannose inhibited glutamine uptake but glucose, galactose, and fructose did not. In addition to respiratory inhibitors, N-ethylmaleimide inhibited glutamine uptake. Ouabain did not affect glutamine uptake.
Stewart
C R
CR
Department of Botany and Plant Pathology, Iowa State University, Ames, Iowa 50010.