ABSTRACT
Aminopeptidase A (Pep A) is a metal-dependent enzyme that specifically hydrolyze peptides with the N-terminal amino acids glutamic acid (Glu) and aspartic acid (Asp). A possible application of PepA is the hydrolysis of Glu/Asp-rich food proteins such as wheat gluten and casein, increasing the flavor and solubility of food protein. In the present study, the gene encoding a Pep A from Lactococcus lactis ssp. lactis IL1403 was synthesized and introduced into Pichia pastoris GS115 (His4). Lc-Pep A was successfully expressed and secreted to the culture medium, followed by identification and purification to homogeneity. Characteristics study demonstrated that Lc-Pep A could specifically hydrolyze the substrates Glu-pNA and Asp-pNA with similar catalytic activity, and this was further confirmed by the kinetics parameters measured. Additionally, Lc-Pep A showed a broad thermostability and pH stability with an optimum temperature of 60 ℃ and an optimum pH of 8.0. The enzyme activity of Lc-Pep A was activated by metal ions Co2+, Mn2+, and Zn2+ but was strongly inhibited by Ni2+and Cu2+. The routine proteinase inhibitor had no effect on the activity of Lc-Pep A. However, Lc-Pep A was strongly inhibited by the metallopeptidase inhibitor, EDTA, and disulfide bond-reducing agents. The study may facilitate production and application of Lc-Pep A.
Subject(s)
Glutamyl Aminopeptidase , Lactococcus lactis/genetics , Biological Transport , Culture Media , Glutamic AcidABSTRACT
potato. The rates for removing nitrite also showed the same order.A new compound formed from the reaction of allyl mercaptan with sodium nitrite had characteristic absorption peaks of -NO group at 1508 CM-1 and 650 CM-1 of infrared spectrum. With UV-ray irradiating this new compound, the NO7 radical was regenerated. UV/Vis spectrum scanning also showed the specific absorption of R-SNO compounds. Based on the facts mentioned above and the rules by which -SH compounds react with nitrite to form R-SNO compounds, the molecular structure of this new compound can be described as CH2= CH-CH2-SNO, named "Allylthionitrite".In conclusion, -SH compounds in garlic extract could be competitively reacted with nitrite forming thionitrite compounds and then blocked the formation of nitrosamines. We believed this might be the partial mechanism of the blocking effect of garlic on the formation of nitrosamines.
ABSTRACT
It is well known that some moulds can mediate the formation o NO-com-pounds (NOC), but there have been few means to block its action. In this paper, we introduce garlic extract that can block moulds-mediated nitrosa-tion.Fusarium moniliforme and Aspergillus versicolor were inoculated in Cza-pek's liquid medium with nitrite and diethylamine ordibutylamine added (test group). The concentrations of NDEA and NDBA were higher in the test group than those in the control group (moulds not inoculated), (P
ABSTRACT
In the present study, it has been found that garlic extract has the ability of blocking the formation of DMN, DEN and DBN in vitro under the conditions simulating those of gastric juice. There are very good dose-response relationships between the dosage of garlic extract and the blocking effect on the formation of DEN and DBN.The concentration of nitrite can be lowered with garlic extract. The dosage of garlic extract and the remains of nitrite show highly significant negative correlations. This may be partial mechanism of blocking effect of garlic extract on the formation of nitrosamines.