The factor V-activating enzyme (RVV-V) from Russell's viper venom. Identification of isoproteins RVV-V(α), -Vβ, and -Vγ and their complete amino acid sequences

The complete amino acid sequences of two isoproteins of the factor V-activating enzyme (RVV-V) isolated from Vipera russelli (Russell's viper) venom were determined by sequencing S-pyridylethylated derivatives of the proteins and their peptide fragments generated by either chemical (cyanogen bromide and 2-(2-nitrophenylsulfenyl)-3-methyl-3-bromoindolenine) or enzymatic (trypsin, α-chymotrypsin, and lysyl endopeptidase) cleavages. Both enzymes, designated RVV-Vα and RVV-Vγ, consist of 236 amino acid residues and have a N-linked oligosaccharide chain at Asn²²⁹. The six amino acid substitutions between RVV-Vα and -Vγ are: Thr²²(α)-Ala²²(γ), Gly²⁹(α)-Ala²⁹(γ), Gln¹⁹¹(α)-Glu¹⁹¹(γ), Ile¹⁹²(α)-Met¹⁹²(γ), Gln¹⁹³(α)-His¹⁹³(γ), and Asn²²⁴(α)-Ser²²⁴(γ). The molecular weights were calculated as 26,182 for RVV-Vα and 26,167 for RVV-Vγ. The sequences of the RVV-V isoproteins exhibited 62% identity with that of batroxobin, a thrombin-like enzyme present in Bothrops atrox venom, and 33% identity with that of human thrombin B chain. The most interesting difference between the structures of RVV-V and other trypsin-type serine proteases is that the conservative Ser²¹⁴-Trp²¹⁵-Gly²¹⁶ sequence (chymotyrpsinogen numbering), considered as the site of antiparallel β-sheet formation between the protein substrate and most serine proteases, has been replaced by the corresponding sequence Ala-Gly-Gly.