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Differential Sensitivity of Basal and Opioid‐Stimulated Low K m GTPase to Guanine Nucleotide Analogs
Author(s) -
Vachon Luc,
Costa Tommaso,
Herz Albert
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00766.x
Subject(s) - guanine , nucleotide , gtpase , sensitivity (control systems) , differential (mechanical device) , chemistry , basal (medicine) , opioid , biophysics , stereochemistry , endocrinology , medicine , biology , biochemistry , receptor , physics , gene , electronic engineering , insulin , engineering , thermodynamics
In membranes derived from NG108–15 cells, the opioid peptide [D‐Ala 2 ,D‐Leu 5 ]enkephaIin (DADLE) stimulates a low K m GTPase. The nucleotide analogs guanosine 5′‐ O ‐(2‐thio)diphosphate (GDPβS), guanosine 5′‐(β,γ‐imi‐do)triphosphate [Gpp(NH)p] and guanosine 5′‐ O ‐(3‐thio)‐triphosphate (GTPγS) inhibit the basal enzymatic activity with the order of potency GTPγS > Gpp (NH)p > GDPβS. In the presence of DADLE, the inhibition isotherms of GDPβS and Gpp(NH)p are shifted to the right five‐ and fourfold, respectively, compared to the inhibition observed in the absence of DADLE. In contrast, the IC 50 of GTPγS for inhibiting the enzyme is reduced by 55% in the presence of the opioid. Both Gpp(NH)p and GTPγS produce a concentration‐dependent increase in the K m(app) of GTPase. without affecting its V max , indicating a competitive inhlbi‐tion. However, the replots of K m(app) versus inhibitor concentration are hyperbolic, suggesting a partial type of inhibi‐tion. Both Gpp(NH)p and GTPγS, but not GTP, induce an increase in the EC 50 of DADLE for stimulating GTPase These findings indicate that the basal and the opioid‐stimu‐lated low K m GTPase differ in their respective sensitivities to inhibition by guanine nucleotide analogs.