Enzymatic degradation of GTP and its "stable" analogues produce apparent isomerization of opioid receptors.
GTP reduces the affinity of agonists to opioid receptors in membranes from NG 108-15 cells. This can be demonstrated using a short incubation time in equilibrium binding and in dissociation experiments: GTP decreases equilibrium binding, increases the percentage of fast dissociating binding and produces a conversion of high into low affinity receptors. However, upon prolonged incubation time (more than 60 min) these effects of GTP are gradually lost. This loss of guanine nucleotide effect is also observed with other nucleotides, namely GDP, GTP gamma S and GppNHp. Incubation of radioactive GTP with membranes and subsequent analysis of the guanine nucleotides by TLC (thin layer chromatography) reveals that GTP is rapidly hydrolyzed to GDP and thereupon to the inactive nucleotide GMP and guanosine. The so-called "hydrolysis-resistant" analogues of GTP, GTP gamma S and GppNHp are also degraded under these experimental conditions. The hydrolysis is apparent with membranes from different tissues and occurs with half times of less than 5 min for GTP and of 10 - 30 min for GDP and "stable" GTP-analogues. Conditions that reduce the degradation of guanine nucleotides during incubation with membranes are described.
Ott
S
S
Max-Planck-Institut fuer Psychiatrie, Abteilung Neuropharmakologie, Martinsried, FRG.
Costa
T
T
D000818:Animals; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000378:metabolism; D016308:Enkephalin, Leucine-2-Alanine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism / Q000494:pharmacology; D006868:Hydrolysis; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D013873:Thionucleotides / Q000378:metabolism / Q000494:pharmacology
D011957:Receptors, Opioid; D013873:Thionucleotides; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine; D006160:Guanosine Triphosphate; D008274:Magnesium