title: Purification and kinetics of two novel thermophilic extracellular proteases from Lactobacillus helveticus, from kefir with possible biotechnological interest.
abstract: Two thermophilic extracellular proteases, designated Lmm-protease-Lh ( approximately 29 kDa) and Hmm-protease-Lh ( approximately 62 kDa), were purified from the Lactobacillus helveticus from kefir, and found active in media containing dithiothreitol; the activity of Lmm-protease-Lh was increased significantly in media containing also EDTAK(2). Both novel proteases maintained full activity at 60 degrees C after 1-h incubation at 10 degrees C as well as at 80 degrees C, showing optimum k(cat)/K(m) values at pH 7.00 and 60 degrees C. Only irreversible inhibitors specific for cysteine proteinases strongly inhibited the activity of both novel enzymes, while they remained unaffected by irreversible inhibitors specific for serine proteinases. Both enzymes hydrolyzed the substrate Suc-FR-pNA via Michaelis-Menten kinetics; conversely, the substrate Cbz-FR-pNA was hydrolyzed by Lmm-protease-Lh via Michaelis-Menten kinetics and by Hmm-protease-Lh via substrate inhibition kinetics. Valuable rate constants and activation energies were estimated from the temperature-(k(cat)/K(m)) profiles of both enzymes, and useful results were obtained from the effect of different metallic ions on their Michaelis-Menten parameters.
authors.affiliation: University of Ioannina, Department of Chemistry, Sector of Organic Chemistry and Biochemistry, Laboratory of Enzymology, Ioannina 45110, Greece.
authors.forename: Krystalenia
authors.initials: K
authors.lastname: Valasaki
authors.forename: Aggeliki
authors.initials: A
authors.lastname: Staikou
authors.forename: Leonidas G
authors.initials: LG
authors.lastname: Theodorou
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Charamopoulou
authors.forename: Paraskevi
authors.initials: P
authors.lastname: Zacharaki
authors.forename: Emmanuel M
authors.initials: EM
authors.lastname: Papamichael
mesh_terms: D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism; D043302:Cultured Milk Products / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D052198:Lactobacillus helveticus / Q000201:enzymology* / Q000302:isolation & purification; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D010447:Peptide Hydrolases