Endoproteinase Lys-C is a serine protease isolated from Lysobacter enzymogenes as a highly purified protease that hydrolyzes specifically at the carboxyl side of Lys. Lys-C retains proteolytic activity under protein denaturing conditions such as 8M urea, which is used to improve digestion of proteolytically resistant proteins. Lys-C activity is optimal in the pH range of 7.0Ñ9.0. This protease can be used alone or in combination with other proteases to produce protein digests for peptide mapping applications or protein identification by peptide mass fingerprinting or MS/MS spectral matching. Endoproteinase Lys-N is a metalloprotease that cleaves at the amino side of lysine residues. Lys-N is a zinc metalloprotease derived from Grifola frondosa that retains proteolytic activity under protein denaturing conditions such as 8M urea, which is used to improve digestion of proteolytically resistant proteins. Charged amino-terminal peptide fragments generated by Lys-N are useful for de novo sequencing with ETD fragmentation techniques.
