Effect of synthetic purines and purine nucleosides on [3H]diazepam binding in brain

We have compared fifteen synthetic purines and purine nucleosides on their ability to displace [3H]diazepam binding to rat brain membranes. Among these analogs, 6-methylthioguanine was found to be most potent, inhibiting competitively the specific binding of [3H]diazepam with a Ki value of 16 micro M. At a concentration of 50 micro M, 6-methyl-thioguanine increased tha apparent Kd of specific diazepam binding from 4.3 nM to 13.3 nM without affecting the Bmax, nor had it any effect on the non-specific binding. Binding with membrane preparations from developing rat brain was slightly less sensitive to 6-methylthioguanine inhibition than that with membranes prepared from mature brain.