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Characterisation of an Allosteric Modulatory Protein Associated with α‐[ 3 H]Amino‐3‐Hydroxy‐5‐Methylisoxazolepropionate Binding Sites in Chick Telencephalon: Effects of High‐Energy Radiation and Detergent Solubilisation
Author(s) -
Henley Jeremy M.,
Nielsen Mogens,
Barnard Eric A.
Publication year - 1992
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.1471-4159.1992.tb10943.x
Subject(s) - cerebrum , ampa receptor , allosteric regulation , chemistry , binding site , biochemistry , biophysics , glutamate receptor , biology , receptor , central nervous system , endocrinology
α‐[ 3 H]Amino‐3‐hydroxy‐5‐methylisoxazolepro‐pionate ([ 3 H]AMPA) binds to 1‐day‐old chick telencephalon membranes with K D and B max values of 138 n M and 2.56 pmol/mg of protein, respectively. High‐energy radiation bombardment of intact frozen telencephalon resulted in a biphasic inactivation curve for [ 3 H]AMPA binding. At a 5.8‐Mrad radiation dose, the affinity of [ 3 H]AMPA binding was increased (54 n M ), but there was no apparent alteration in the B max value (2.76 pmol/mg of protein). We attribute this phenomenon to the inactivation of a high molecular weight modulatory protein that down‐regulates the affinity of [ 3 H]AMPA binding. The estimated molecular masses of the AMPA binding site and of the modulatory component were 59 and 108 kDa, respectively. Solubilisation with n ‐octyl‐β‐glucopyranoside resulted in an increase in the B max (4.7 pmol/ mg of protein) with no pronounced alteration in the affinity (109 n M ) of [ 3 H]AMPA binding. However, the solubilisation‐induced increase in B max did not occur in telencephalon irradiated before solubilisation. In contrast, the increase in affinity induced by radiation treatment was still detected in solubilised extracts. These results suggest that the number and affinity of [ 3 H]AMPA sites in chick telencephalon are closely regulated and that the modulatory systems involved are affected by both irradiation and solubilisation.