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Abstract
The geographic variations of phospholipases A2 (PLAs) in the venom of four medically important pit vipers were investigated. We have studied the PLAs by HPLC‐purification, cDNA cloning and sequencing, mass characterization, and functional classification. We found that: 1) Anti‐platelet acidic PLA isoforms in the venoms of Calloselasma rhodostoma from five southeastern Asian countries, and those of the Crotalus v. viridis from seven American States are differentially expressed depending on locality. The variations could be attributed to their distinct specificities towards the platelets of different prey, and to possible adaptation for playing other functional roles. In contrast, structures of the myonecrotic and the edema‐inducing basic PLAs in both venoms were relatively conserved. 2) A special type of the acidic anti‐platelet PLA is present in the venom of some Protobothrops species. Its expression level is diminished in the snake of the southern or the tropical ranges. 3) The venom of Bamboo tree vipers (Trimeresurus stejnegeri) in Taiwan and China showed extraordinary geographic variations in their acidic and basic PLAs. The high RNA‐polymorphism of their venom proteins may have been derived from interbreeding between several ancestral pit viper species. In addition, migration, isolation of different populations and rapid evolution of the venom proteins to adapt for diversified diets may have resulted in further variations in this venom species.