BIOCHEMICAL STUDIES ON THE TOXIC NATURE OF SNAKE VENOM
Rept. no. 2 (Final), Jun 1967-Jun 1968
KAOHSIUNG MEDICAL COLL (TAIWAN) DEPT OF BIOCHEMISTRY
Pagination or Media Count:
The exhausted iodination of cobrotoxin, the crystalline toxin obtained from Formosan cobra venom, with I131 resulted in the maximum incorporation of 4 moles iodine per mole toxin without changing its lethality or antigenicity. The scanogram of rabbits in both conditions, immunized and non- immunized, showed marked different pattern in distribution of radioactivity. Sixty-six per cent of the injected radioactivity was demonstrated in the liver of the immunized rabbit, sacrified 5 hours after injection of the labeled toxin. In the non-immunized rabbit the radioactivity was localized in the bladder 2 hours after injection. The optical rotatory dispersion ORD curve of the native cobrotoxin is quite different from those of the usual proteins having right-handed alpha-helical structure and has a positive peak at 207 millimicrons, a negative trough at 222 millimicrons, and a large positive peak at 233 millimicrons. The very unusual ORD curve with a positive peak at 233 millimicrons and a negative trough at 222 millimicrons has been observed so far only for avidin and erabutoxin a. The Circular Dichroism CD spectrum of cobrotoxin had negative maxima at around 285 millimicrons and 215 millimicrons, and positive maxima at 228 millimicrons and at around 201 millimicrons. It is suggested that the cobrotoxin molecule contains beta-structure. On reduction or oxidation of the disulfide bonds, the ORD and CD curves changed greatly. These ORD and CD curves are not characteristic of the completely random conformation, but closely resemble the calculated ORD curves of a mixture of a large amount of random coil and a small amount of alpha-helix or beta-structure.