Further characterization of the anticoagulant proteinase, cerastase F-4 from cerastes cerastes (Egyptian sand viper) venom

A potent anticoagulant, cerastase F-4, was purified from the venom of Cerastes cerastes. The u.v. absorption spectrum revealed a relatively high tyrosine and low tryptophan content. The molar extinction coefficient and E 278 0.1% were 19,400 and 0.84, respectively. The enzyme secondary structure, as studied by circular dichroism, showed 23.6% α-helix, 34% β-sheets, 19% β-turns and 32.5% random coils. When casein was used as a substrate of optimum pH was 10.0 and the K m was 1.45 g/I. Cerastase F-4 is a metallo-enzyme that contains one mole of Ca 2+ and one of Zn 2+ per mole of protein. It is not affected by phenylmethane sulfonylfluoride or soybean trypsin inhibitor, while it is completely inhibited by 0.5 mM EDTA or ethyleneglycol bis (β-amino ethylether) N, N, N′, N′- tetraacetic acid (EGTA). Ca 2+, Mg 2+ and Zn 2+ partially activated by the enzyme under different experimental conditions. Our results suggest that Ca 2+ and Zn 2+ may play a role in maintaining the structural and catalytic integrity of the enzyme.