title: Enzyme activities of cell-free extracts from mutant strains of lactic streptococci subjected to sublethal heating or freeze-thawing.
abstract: Two mutant lactose-negative (Lac-), proteinase-negative (Prt-) strains of lactic streptococci, Streptococcus lactis 25Sp and S. cremoris KHA2, and their parents, S. lactis C2 and S. cremoris KH Lac+ Prt+, were grown in a suitable medium with the pH maintained at 6.5 by addition of NH4OH. Cells were harvested by centrifugation, resuspended, and then heated sublethally at 54 or 69 degrees C for 15 sec. Cells also were frozen and stored for 1 week at -20 or -100 degrees C. Cell-free extracts of cells heated at 54 degrees C had more proteinase and aminopeptidase activities than did a similar extract of cells heated at 69 degrees C. The greatest enzyme activities occurred in the cell-free extracts prepared from cells frozen and stored at -100 degrees C. Specific activities of proteinase and dipeptidase generally decreased in extracts of freeze-shocked cells compared to those in extracts of untreated cells. Enzyme activity of extracts also decreased in the presence of 5% NaCl at pH 5.0. Cell-free extracts at pH values of 5 to 8 were heated at 69 degrees C for 1.5, or 10 min. Heating them for 10 min caused a loss of dipeptidase activity which was most pronounced at pH 5.0 and least pronounced at pH 7.0.
authors.affiliation: Department of Food Science, University of Wisconsin, Madison, Wisconsin 53706.
authors.forename: K M
authors.initials: KM
authors.lastname: Kamaly
authors.forename: E H
authors.initials: EH
authors.lastname: Marth
mesh_terms: D000626:Aminopeptidases / Q000378:metabolism; D004150:Dipeptidases / Q000378:metabolism; D004355:Drug Stability; D010450:Endopeptidases / Q000378:metabolism; D005615:Freezing; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D013294:Lactococcus lactis / Q000201:enzymology* / Q000235:genetics; D007785:Lactose / Q000378:metabolism; D008854:Microscopy, Electron; D009154:Mutation; D013291:Streptococcus / Q000201:enzymology* / Q000235:genetics
chemical_list: D010450:Endopeptidases; D000626:Aminopeptidases; D004150:Dipeptidases; D007785:Lactose