. "Proteolytic enzyme with a cysteine residue (Cys) in its active site. There are many families of thiol proteases. The most well known one is the papain family (C1 in MEROPS classification) which is known to exist in most eukaryotes." . . "Thiol protease" . "Thiol peptidase" . "Thiol proteinase" . "Sulfhydryl protease" . . .