Studies on the Active Site of IRC‐50 Arvin, the Purified Coagulant Enzyme from Agkistrodon rhodostoma Venom

A number of the properties of the active site of IRC‐50 arvin, a coagulant enzyme from Agkistrodon rhodostoma , have been studied. The results indicate that the enzyme is in many ways similar to the mammalian serine proteinases.1 IRC‐50 arvin will hydrolyse α‐ N ‐benzoyl‐L‐arginine esters and a study of the rates of hydrolysis of a number of these esters indicates that the hydolysis may proceed via a common acylenzyme intermediate. 2 IRC‐50 arvin is inactivated by di‐isopropylfluorophosphate and phenylmethanesulphonyl fluoride but at much lower rates than the mammalian serine proteinases. 3 Both the catalytic activity and rate of inactivation of the enzyme by di‐isopropylfluorophosphate and phenylmethanesulphonyl fluoride are dependent on the ionisation of a group with pK (app) ∼ 7.0; this group is probably a histidine residue. 4 Evidence is presented which suggests that the esterase and coagulant activity of the enzyme are associated with the same active site. 5 Titration of the active site of the enzyme with p′ ‐nitrophenol p′ ‐guanidinobenzoate demonstrates that IRC‐50 arvin has one active site per mole, based on a molecular weight of 55000.