EFFECT OF CHEMICAL MODIFICATION OF ARGINYL AND HISTIDYL RESIDUES ON [H-3] MK-801 BINDING TO BRAIN SYNAPTIC-MEMBRANES

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 of [H-3]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 [H-3]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.