Abstract
A specific binding activity for phenytoin (PHT) was determined by a modified receptor assay with 3H-PHT using the ammonium sulfate precipitation and the glass filter filtration method. Approximately 70% of the specific binding activity was observed to exist in particulate fractions of the rat brain. Approximately 40% of the binding activity in the particulates was solubilized by freezing-thawing, ultrasonication and detergent CHAPS (3-[(3-cholamidopropyl) dimethylamino]-1-propanesulfonate) treatments. The solubilized binding sites were partially purified by Phenyl-Sepharose gel chromatography and n-butanol treatment, and it was found that a specific binding activity/protein of the purified fraction increased up to about ten times as much as the activity with non-purified solubilized fraction.
The PHT, related hydantoins and barbiturates were compared in terms of their affinity for the PHT binding sites. It was found that PHT and MPPH (5-(p-methylphenyl)-5-phenylhydantoin) indicated the highest affinity among the drugs tested. The affinity of HPPH (5-(p-hydroxyphenyl)-5-phenylhydantoin), whose hydrophilic hydroxyl group is substituted for the methyl group of MPPH, was markedly decreased as compared to that of MPPH. Almost no affinity was shown in the case of ethotoin, pentobarbital and phenobarbital. It is proposed that the PHT binding sites prepared in this study recognize quite specifically the particular chemical structure of the drug.
