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Removal of N-terminal blocking groups from proteins.

Current protocols in protein science / editorial board, John E. Coligan ... [et al.], ISSN: 1934-3663, Vol: Chapter 11, Issue: 1, Page: Unit 11.7
2001
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Two enzymatic methods commonly used in N-terminal sequence analysis of blocked proteins are presented in this unit; one uses pyroglutamate aminopeptidase for N(alpha)-pyrrolidone carboxyl-proteins in solution or blotted onto a membrane, and the other uses acylaminoacyl-peptide hydrolase for N(alpha)-acyl-proteins blocked with other acyl groups. A Support Protocol describes a colorimetric assay for pyroglutamate aminopeptidase activity. Sequencing with acylaminoacyl-peptide hydrolase must include fragmentation of the protein before unblocking can be carried out, so procedures are provided for chemically blocking newly generated peptides with either succinic anhydride or phenylisothiocyanate/performic acid. The hydrolase is then applied to the total mixture of peptides, only one of which, the acylated N-terminal peptide, should be a substrate for hydrolase. After incubation, the mixture of peptides is subjected to sequence analysis. Protocols are also provided for unblocking N-terminally blocked proteins using acid-catalyzed hydrolysis or methanolysis, hydrazinolysis, and beta-elimination after acid-catalyzed N-O shift. Alternate protocols describe chemical removal of acetyl and longer-chain alkanoyl groups, as well as formyl groups to open the cyclic imide of pyrrolidone carboxylate.

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