عنوان

Proline-specific peptidases from Lactobacillus casei subspecies

Number

TLpq89314391

.Language of Text, Soundtrack etc

انگلیسی

Title Proper

Proline-specific peptidases from Lactobacillus casei subspecies

General Material Designation

[Thesis]

First Statement of Responsibility

M. B. Habibi-Najafi

Subsequent Statement of Responsibility

B. H. Lee

Name of Publisher, Distributor, etc.

McGill University (Canada)

Date of Publication, Distribution, etc.

1994

Specific Material Designation and Extent of Item

216

Dissertation or thesis details and type of degree

Ph.D.

Body granting the degree

McGill University (Canada)

Text preceding or following the note

1994

Text of Note

The objectives of this study were (l) to screen out active proline-specific peptidases from Lactobacillus casei subspecies, (2) to study growth kinetic and enzyme production from enriched medium (MRS) and cheese whey medium, (3) to purify and characterize two active proline-specific enzymes, and (4) to investigate the action of purified enzyme on bitter tryptic digests of usd\betausd-casein as well as bitter enzyme-modified cheese. Lactobacillus casei subsp. casei LLG and Lactobacillus casei subsp. rhamnosus S93 were examined for extra- and intra-cellular proline-specific peptidase activities. Both strains showed strong activity for x-prolyl dipeptidyl peptidase and proline iminopeptidase but had weak activities for prolidase, prolinase, and post proline endopeptidase. Histochemical staining of crude enzyme extract from Lactobacillus casei ssp. casei LLG with different substrates revealed a distinct protein band for x-prolyl dipeptidyl peptidase as well as for proline iminopeptidase. The growth kinetics showed that the intracellular proline-specific peptidases increased gradually at the beginning of the exponential phase and reached a maximum at the beginning of stationary phase. Storage stability of x-prolyl dipeptidyl peptidase and proline iminopeptidase in crude extract, with and without stabilizers showed no significant loss in activity of these two enzymes at 4C for 9 days without adding any stabilizers. The levels of x-prolyl dipeptidyl peptidase, proline iminopeptidase, and post proline endopeptidase activities of cells grown in whey did not vary markedly from cells grown in MRS broth. X-prolyl dipeptidyl peptidase and proline iminopeptidase were purified from crude cell-free extract of Lactobacillus casei ssp. casei LLG by Fast Protein Liquid Chromatography (FPLC) equipped with ion-exchange and gel-filtration columns. X-prolyl dipeptidyl peptidase was found to be a serine-dependent enzyme with molecular mass of 79 kDa. The pH and the temperature optima by the purified enzyme were 7.0 and 50C, respectively. Proline iminopeptidase was sulfhydryl enzyme with molecular mass of 46 kDa. The maximum enzyme activity was observed at pH 7.5 and 40C. This is the first report describing the purification and characterization of x-prolyl dipeptidyl peptidase and proline iminopeptidase from Lactobacillus casei to homogeneity. The debittering of tryptic digests from usd\betausd-casein by x-prolyl dipeptidyl peptidase was studied by reversed phase high performance liquid chromatography (RP-HPLC) and liquid chromatography/mass spectrometry. The results showed that two bitter peptides (f53-97 and f03-209) containing X-Pro-Y-Pro in their amino acid residues were completely hydrolyzed and many other peptides with high hydrophobicity were decreased in peak area. The addition of purified x-prolyl dipeptidyl peptidase on bitter enzyme-modified cheese (EMC) also showed that at least one bitter peptide with X-Pro-Y derived from usd\alphausd-casein hydrolysis was removed.

Biological sciences

Food science

Food science

Microbiology

B. H. Lee

M. B. Habibi-Najafi

Electronic name

p

[Thesis]

276903

a

Y