title: Effects of guanine nucleotides, transition metals and temperature on enkephalin receptors of rat brain membranes.
abstract: The interactions among guanine nucleotides, transition metals and enkephalin (ENK) receptors were investigated by assaying the [3H]ENK binding to brain synaptic membranes. In the presence of 100 mM NaCl, GTP and Gpp(NH)p reduced the binding of [3H]ENK at 0 degree C and 25 degrees C, reflecting a decrease mainly in the affinity of the binding sites. In the absence of sodium, however, guanine nucleotides only slightly lowered the ENK binding at 25 degrees C, and at 0 degree C they strongly increased the ENK binding dose-dependently. This nucleotide-induced increase of specific ENK binding reflects an increase in the affinity and the number of the binding sites. In micromolar concentrations, zinc and cupric ions inhibited the ENK binding to opioid receptors by respectively reducing the affinity and the number of binding sites. In the absence of sodium at 0 degree C, cupric ions completely antagonized the nucleotide-induced increase in the ENK binding, although zinc ions did not affect it. The results suggest complex interactions of transition metals and guanine nucleotides with ENK binding sites.
mesh_terms: D000227:Adenine Nucleotides / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D009270:Naloxone / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics; D015032:Zinc / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D011957:Receptors, Opioid; D009270:Naloxone; D004744:Enkephalin, Methionine; C022118:enkephalinamide-Met, Ala(2)-; D003300:Copper; D015032:Zinc