Kinetics of Binding of [³H]Glycine to Transport Proteins in Channel Catfish Brain

Abstract

[³H]Glycine was observed to bind to channel catfish brain particles in a manner displaying saturation kinetics. The dissociation constant was calculated to be 7.38 ± 2.11 µM. Though some binding occurred in the absence of Na⁺ ions, the presence of such ions stimulated binding in a concentration-dependent manner. Similarly, chloride ions had a stimulatory effect on [³H]glycine binding. Several inhibitors of binding were identified, the most effective being β-alanine, pipecolic acid, 2,3-pyrazine dicarboxylic acid and 3,5-pyrazole dicarboxylic acid. Each is a structural analogue of glycine. Harmaline, a known inhibitor of Na⁺ binding, also inhibited glycine binding. A previous study had shown the presence of a sodium-dependent, active uptake system for glycine in synaptosomes derived from catfish brain. The present results suggest that the binding of [³H]glycine was to a glycine transporter and that the amino acid functions as a neurotransmitter in this species.

Irreversible Inhibition of [³H]Glycine Transport into Channel Catfish Erythrocytes by Thiol Group Modifiers

“…in channel catfish both nervous tissue and erythrocytes can transport glycine via GLYT [9][10][11]. This report demonstrates that GLYT in red blood cells of channel catfish can be inactivated by thiol group reagents, suggesting that cysteinyl residues play a key role in the glycine transport.…”

Membrane Glycine Transport Proteins

“…This uptake of glycine required Na + ions and bore the hallmark of a secondary active process reminiscent of system Gly. A similar glycine transport system has been examined in the brain of channel catfish [1,82]. Just over a decade ago, Ló pez-Corcuera et al [52] purified a glycine transporter from pig brainstem with a molecular weight of 100 kD.…”