Effect of chemical modification of arginyl and histidyl residues on [ 3H]MK-801 binding to brain synaptic membranes

Abstract

Chemical modification of the N- methyl- d-aspartate (NMDA) receptor was investigated in a thoroughly washed Triton-treated pig forebrain membrane preparation. Modification of arginyl residues using phenylglyoxal significantly reduced activation of the NMDA receptor as measured by specific binding [ 3H]MK-801 [(+)-5-methyl-10,11-dihydro-dibenzo[ a, d]cyclohepten-5,10-imine]. The reduction was due to a decrease in the affinity of MK-801 for its binding site from 3.2 ± 0.5 nM to 22 ± 8 nM. Protection studies indicated that alteration of the glutamate or glycine binding sites is not directly responsible for the effect. Diethyl pyrocarbonate treatment also reduced [ 3H]MK-801 binding, by modification of histidyl residues. The binding affinity was reduced to 8.3 ± 1.4 nM whereas the B max was unchanged. Protection studies indicated that the modified histidine is unlikely to be a component of the glutamate, glycine or MK-801 binding sites. However, the accessibility of the modified histidine seems to be partly dependent on the activation state of the receptor.