Effect of purified phospholipases on the binding of tetrodotoxin to axon plasma membrane.

The role of phospholipids in the binding of [3H]tetrodotoxin to garfish olfactory nerve axon plasma membrane was studied by the use of purified phospholipases. Treatment of the membranes with low concentrations of either phospholipase A2 (Crotalus adamanteus and Naja naja) or phospholipase C (Bacillus cereus and Clostridium perfringens) resulted in a marked reduction in tetrodotoxin binding activity. A 90% reduction in the activity occurred with about 45% hydrolysis of membrane phospholipids by phospholipase A2, and with phospholipase C the lipid hydrolysis was about 60--70% for a 70--80% reduction in the binding activity. Phospholipase C from B. cereus and Cl. perfringens had similar inhibitory effects. Bovine serum albumin protected the tetrodotoxin binding activity of the membrane from the inhibitory effect of phospholipase A2 but not from that of phospholipase C. In the presence of albumin about 25% of the membrane phospholipids remained unhydrolyzed by phospholipase A2. It is suggested that these unhydrolyzed phospholipids are in a physical state different from the rest of the membrane phospholipids and that these include the phospholipids which are directly related to the tetrodotoxin binding component. It is concluded that phospholipids form an integral part of the tetrodotoxin binding component of the axon membrane and that the phospholipase-caused inhibition of the binding activity is due to effects resulting from alteration of the phospholipid components.