Discrimination of envenomated prey is not dependent on enzymatic toxins. (A) Size exclusion fractionation of 250 mg crude C. atrox venom on a 90 × 2.8 cm BioGel P-100 column equilibrated with HEPES/NaCl/CaCl2 buffer. Fractionation occurred at a flow rate of 6.3 mL per hour at 4°C, and eluting proteins/peptides were followed by absorbance at 280 nm. Enzyme activities common to rattlesnake venoms were assayed and are limited to the first two peaks. Arrow indicates the peak containing crotatroxins 1 and 2 (Peak III). (B) MALDI-TOF-MS analysis of peptides in BioGel size exclusion Peak III. Approximately 0.5 μg protein was spotted onto sinapinic acid matrix and analyzed using a mass window of 3 to 25 kD. Several peptides with masses typical of monomeric disintegrins (7,245 to 7,655 Da) were present, but no larger proteins were observed.