A study of aminopeptidases from lactic streptococci : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biochemistry at Massey University

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dc.contributor.authorLloyd, Richard John
dc.date.accessioned2019-03-22T01:00:12Z
dc.date.available2019-03-22T01:00:12Z
dc.date.issued1989
dc.description.abstractTwo arninopeptidase enzymes from the proteolytic system of Streptococcus lactis 4760 have been studied. An X-Prolyl dipeptidyl arninopeptidase has been purified and characterised. The enzyme has a native molecular weight of approximately 150 kDa determined by gel filtration, and a subunit molecular weight of 83 000, determined by denaturing polyacrylarnide gel electrophoresis, showing the native enzyme to be a dimer. It is inhibited by phenyl methyl sulphonyl fluoride and is active over a pH range of 6 - 9. A range of X-Prolyl-amido methyl coumarin (X-Pro-AMC) derivatives with different aminoacyl residues in the X position have been used to define the steady state kinetic parameters. The Km and kcat values obtained with all of the X-Pro-AMC substrates tested were similar, with the exception of Glu-Pro-AMC, which gave a somewhat higher Km value. The action of the enzyme in degrading small peptides has been studied. It was found to be capable of removing X-Proline residues from peptides, except where two proline residues are situated in consecutive positions. A Lysyl-arninopeptidase has been partially purified and its characteristics studied. This enzyme has been shown to have a native molecular weight of approximately 78 000. It hydrolyses lysyl-, arginyl-, and leucyl-arnido methyl coumarin derivatives, but has little or no activity with other arninoacyl-AMC substrates. It also catalyses the removal of lysine and arginine residues from the amino-terminus of short peptides. The partially purified arninopeptidase preparation also has endopeptidase activity which is probably due to contamination by a separate enzyme. The individual and combined effects of these two enzymes on -casein-derived oligopeptides (produced by proteolytic action of the S.lactis proteinase) have been studied. These results indicate that these enzymes may be important in degradation of some casein-derived peptides during cheese ripening, while other peptides are resistant to hydrolysis.en_US
dc.identifier.urihttp://hdl.handle.net/10179/14472
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectAminopeptidasesen_US
dc.subjectMilk proteinsen_US
dc.subjectLactic acid bacteriaen_US
dc.titleA study of aminopeptidases from lactic streptococci : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biochemistry at Massey Universityen_US
dc.typeThesisen_US
massey.contributor.authorLloyd, Richard John
thesis.degree.disciplineBiochemistryen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelMastersen_US
thesis.degree.nameMaster of Science (M. Sc.)en_US
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