Serine protease
Serine proteases ( or serine endopeptidases ) are enzymes that cleave peptide bonds in proteins , in which serine serves as the nucleophilic amino acid at the ( enzyme's ) active site . 
<triplet> enzyme <subj> protein <obj> subclass of <triplet> peptide bond <subj> amino acid <obj> made from material <triplet> protein <subj> peptide bond <obj> has part <subj> amino acid <obj> has part <triplet> active site <subj> enzyme <obj> part of