Taipoxin-binding protein on synaptic membranes: identification by affinity labeling.

Affinity labeling techniques were used to identify the neuronal membrane molecules involved in the binding of taipoxin, a neurotoxic protein with phospholipase A2 activity. After [125I]taipoxin had bound to synaptosomes from guinea pig brain, treatment with disuccinimidyl suberate resulted in the formation of a predominant radioactive conjugate of 60,000 Da. Notexin and some other PLA2s are weakly inhibitory to this conjugation, while beta-bungarotoxin and some others are not inhibitory. The 60K conjugate was not detected when plasma membranes from several nonneuronal tissues were used. We concluded that a 45,000 Da protein specifically present in neuronal membranes is (a subunit of) the major molecule responsible for taipoxin binding.