Interaction of glycine with brain-cortex membrane fragments: kinetics, ionic requirements and amino acid specificity.
The binding of [14]glycine to rat brain-cortex membrane fragments, incubated in artificial cerebrospinal fluid, was studied in vitro by means of a nitrocellulose filter assay. The membranes were obtained from the large granule fraction (P2) of a brain-cortex homogenate, which was osmotically shocked and the larger membrane fractions isolated by centrifugation. Initial binding velocity lasts for about 2 min and equilibrium is reached in 10 min. The binding reaction is reversible, and [14C]glycine can de displaced by an excess of [12C]glycine or by dilution. Binding is strongly dependent on temperature and on sodium ions. The latter activate the binding process in a cooperative manner. Two binding components may be discerned: one with high affinity for glycine (Km = 40 +/- 8 muM) and one with lower affinity. Lowering the sodium concentration to 60 mM increases the Km of the high-affinity component to 59 muM, with no change in Vmax. The bound product is, after incubating the membranes at 37 degrees C for 10 min, 85% glycine. A large fraction of it may released by hypo-osmotic media.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011955:Receptors, Drug; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D011955:Receptors, Drug; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium; D005998:Glycine