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pH Selectivity of N ‐Ethylmaleimide Reactions with Opiate Receptor Complexes in Rat Brain Membranes
Author(s) -
Childers Steven R.,
Jackson Jerry L.
Publication year - 1984
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.1471-4159.1984.tb12857.x
Subject(s) - selectivity , chemistry , n ethylmaleimide , opiate , membrane , biophysics , receptor , biochemistry , biology , catalysis
N ‐Ethylmaleimide (NEM) decreases opiate agonist binding presumably by blocking crucial sulfhydryl (SH) groups at receptor binding sites. At physiological pH, NEM decreased GTP and manganese regulation but increased sodium effects on [ 3 H] d ‐Ala 2 ‐Met 5 ‐enkephalinamide ( d ‐Ala enk) binding to rat brain membranes. To determine the apparent pK values of putative SH groups in opiate receptors that react with NEM, rat brain membranes were incubated with 100–250 μ m NEM in buffers ranging from pH 4.5 to 8.0. Results showed that lowering pH below 6.5 reduced the NEM effect on opiate receptor functions and that the apparent pK values of NEM‐reacting SH groups in binding and regulatory sites ranged between 5.4 to 6.0. Most of the total SH groups in brain membranes continued to react with NEM at low pH, so that when nonspecific SH groups were blocked by incubating membranes at pH 4.5 with NEM, opiate receptors became sensitive to very low concentrations (1 μ m of NEM.