Methods in Molecular Biology • 16 Enzymes of Molecular Biology

CHAPTER 18

Aminopeptidases

Aminopeptidase M (EC 3.4.11.2),

Pyroglutamate Aminopeptidase (EC 3.4.19.3),

and Prolidase (EC 3.4.13.9)

Patricia J. Sweeney and John M. Walker

1. Introduction
   Aminopeptidases are proteolytic enzymes that remove L-amino acids
   sequentially from the amino termini of polypeptide chains. A number
   of aminopeptidases have been isolated, including leucine aminopep-
   tidase from serine kidney cytosol (1), aminopeptidase P from E. coli
   (2), proline iminopeptidase from E. coli, and swine kidney (3), ami-
   nopeptidase B from rat liver (4), and aminopeptidase A from rat kid-
   ney (5). However, three aminopeptidases in particular have found
   routine use in protein chemistry. The first is pyroglutamate aminopep-
   tidase, a thiol exoprotease that cleaves N-terminal pyroglutamyl resi-
   dues (pyrrolidone carboxylic acid) from peptides and proteins (6-10).
   N-terminal glutamine residues can readily cyclize to the pyroglutamyl
   derivative (Fig. 1). This can occur during peptide and protein purifi-
   cation (it is uncertain whether the N-terminal pyroglutamyl residues
   of a number of naturally occurring peptides and proteins are genuine
   posttranslational modifications, or were introduced by cyclization of
   N-terminal glutamine during purification) or during sequence deter-
   mination when glutamine was the newly liberated N-terminal amino
   acid. This cyclized derivative does not have a free amino group, and

From: Methods in Molecular Biology, VoL 16: Enzymes of Molecular Biology

Edited by: M. M. Burrell Copyright ©1993 Humana Press Inc., Totowa, NJ

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