An X-prolyl-dipeptidylaminopep tidase (Pep-XP) was purified from the crude intracellular extract of Lactococcus lactis subsp. cremoris NRRL 634 by ion exchange and gel filtration chromatographies. The enzyme was purified 80-fold with a recovery of 6%, and appeared as a single band with a molecular weight of about 80 kDa on polyacrylamide gel electrophoresis with sodium dodecyl sulphate (SDS-PAGE). The peptidase showed its maximal activity on arginyl-proline-p-nitroanilide at pH 7.0 and at a temperature of 45°C, although there was a good activity of Pep-XP in the pH range of 5.5-7.0 and temperatures between 40 and 50°C. The Michaelis constant (K m ) and the maximum reaction velocity (V max ) values were 0.92 mM and 7.9 U/mg protein min, respectively. The activity of Pep-XP was completely inhibited by phenylmethanesulphonyl fluoride, an inhibitor of serine peptidases, and metal chelators had little effect on enzyme activity. The purified enzyme hydrolyzed synthetic substrates whose structure is X-Pro-Y like Lys-Pro-pNA, but did not hydrolyse Pro-pNA or azocasein, showing that the enzyme did not have aminopeptidase or endopeptidase activities.
Seal packaging of individual fruits of Dancy mandarin ( Citrus reticulata) with polyolefin (0.019 mm) and PVC (0.025 mm) significantly delayed their deterioration, and maintained firmer fruits with bet ter appearance than non-sealed fruits. The films were applied to fruits that had received conventional treatments of washing and disinfection, after which the fruits were stored with non-sealed fruits under refrigeration conditions (5 and 10 °C) during eight weeks plus six days at 20 °C. The results showed that the weight loss and deformation were significantly reduced by the effect of plastic films, at both storage temperatures. Furthermore, significant reductions in the internal atmosphere (CO, content) and ethanol content were observed in sealed fruits. In the sensory evaluation, the juice of sealed fruits showed a fresh flavor at the end of storage, whereas the juice of non-sealed fruits held at 10 °C developed off-flavors. The ripening index (°Brix/acidity ratio) increased significantly only in sealed fruits held at 10°C. The color index was not significantly modified by the effect of plastic films. However, the vitamin C content was significantly lower in sealed fruits at both storage temperatures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.