There arethree thiol consensus patterns: (Gln-X(3)-[Gly]-X-Cys-Trp-X(2)-[Ser, Gly]-[Ser Thr Ala]); ([Gly]-X-His-[Gly Ala]-[Ile Val]-X-[LeuIle Val](2)-Gly-X-[Gly]); ([Tyr]-[Trp]-[Leu]-x-[Ala]-Ans-[Ser]-Trp-x(3)-[Trp]-Gly-x(2)-Gly-[Leu Tyr]-[Phe]-x-[Ile Met]) where X is anyamino acid residue, and the active site residues (Cys, His, Asn)are highly conserved in the sequences of Schistosome cathepsin B(Fig. 3).