Cobra (Naja naja atra) membrane toxin isoforms: Structure and function

Two membrane toxins, termed MT-I and MT-II, were purified to HPLC homogenei ty from the venom of Naja naja atra. The NH2-terminal sequences of the two isoforms were determined. When compared with the known sequences of membran e toxins, we concluded they are CTX-I and CTX-III (from Naja naja atra), re spectively. Membrane toxins are basic peptides typified by a chain of 60 am ino acids long. Their pI is about 10 and Mr is 6,000-7,000. About half of t he amino acids are hydrophobic. There is lytic synergism between membrane toxins and phospholipase A(2). Me mbrane toxins, which are different from neurotoxins, are capable of depolar izing muscle cells. The toxins are able to kill cancer cells in vitro. Elec trocardiograph of cat to which membrane toxin was applied shows magnificent changes. A positive correlation exists between hydrophobicities and activi ties of the toxins to inhibit protein kinase C (PKC) activity. All the effe cts are the result of action of the toxins on cell membranes. In addition, structure-activity relationships are investigated with the available compar ative data for membrane toxins centering on LD,, erythrocyte lysis, and mus cle cell depolarization.