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Purification and characterization of aminopeptidase P from Lactococcus lactis subsp. cremoris

Published online by Cambridge University Press:  01 August 1997

MAEVE McDONNELL
Affiliation:
Biochemistry Department, University College Galway, Irish Republic
RICHARD FITZGERALD
Affiliation:
National Dairy Products Research Centre, Moorepark, Fermoy, Irish Republic
IDE NI FHAOLÁIN
Affiliation:
Department of Life Sciences, Regional Technical College, Galway, Irish Republic
P. VINCENT JENNINGS
Affiliation:
Department of Life Sciences, Regional Technical College, Galway, Irish Republic
GERARD O'CUINN
Affiliation:
Department of Life Sciences, Regional Technical College, Galway, Irish Republic

Abstract

Aminopeptidase P was purified 65·3-fold from the cytoplasm of Lactococcus lactis subsp. cremoris AM2 with a 5·8% yield. The purified enzyme was found to consist of one polypeptide chain with a relative molecular mass of 41600. Metal chelating agents were found to be inhibitory and Mn2+ and Co2+ stimulated activity 7-fold and 6-fold respectively. The purified enzyme removed the N-terminal amino acid from peptides only where proline (and in one case alanine) was present in the penultimate position. No hydrolysis was observed either with dipeptides even when proline was present in the C-terminal position or when either N-terminal proline or pyroglutamate was present preceding a proline residue in the penultimate position of longer peptides. On the basis of this substrate specificity either aminopeptidase P or post-proline dipeptidyl aminopeptidase are necessary along with a broad specificity aminopeptidase to effect complete hydrolysis of casein-derived peptides containing a single internally placed proline residue. However, both aminopeptidase P and post-proline dipeptidyl aminopeptidase would be required together with a broad specificity aminopeptidase in order to completely hydrolyse casein-derived peptides that contain two internally placed consecutive proline residues. As bitter casein-derived peptides are likely to contain either single prolines or pairs of prolines, aminopeptidase P appears to be an important enzyme for debittering.

Type
Research Article
Copyright
Proprietors of Journal of Dairy Research 1997

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