Selection of mastitis-resistant cows using the production of L-amino acid oxidase

点击翻译按钮获取中文摘要

Characterization of L-amino acid oxidase (LAO) in mouse milkLAO was purified from mouse milk. LAO reacted with L-amino acids in an apparent order of Phe> Met, Tyr> Cys, Leu> His>> other 11 amino acids and produced hydrogen peroxide (H_2O_2) in a dose-and time-dependent manner. An apparent Km was 1.0μM for Phe, 8.1μM for Leu and 20.2μM for His. LAO in milk had a molecular weight of 113 kDa and was converted to a 60-kDa protein by SDS-PAGE. By ion-exchange chromatography, the LAO activity was detected in three different fractions. LAO consisted of two subunits but is electrically heterogeneous. The amino acid sequences of N- and C-terminals, and lysylendopeptidase-digested fragments were the same to those of mouse milk LAO deduced from cDNA. This is the first demonstration showing that LAO is present in milk.Mechanism of Bacterial Killing by Mouse MilkAfter gel-filtration, we detected lactoperoxidase (LPO) activity. Using LAO, LPO and amino acids, H_2O_2 was maintained between 190 and 23 … More 0 nmol/ml from 1 to 4 h. We cultured Escherichia (E) coli, Klebsiella (K) pneumoniae, Staphylococcus (S) aureus, and Streptococcus (S) agalactiae strains. Bacteria increased with a doubling time of 30-40 min. However, S.agalactiae and S.aureus did not grow ; the number of viable bacteria remained the same at 4 h as at 0 h. Escherichia coli and K.pneumoniae grew with doubling times of 98 and 84 min, respectively, and growth was suppressed. Bacterial growth was suppressed in the LAO/LPO/amino acid system.Hydrogen peroxide generating substance in cow milkCow milk contained a H_2O_2 generating substance. After gel-filtration, the fraction with a molecular weight of 20 kDa had H_2O_2 generating activity, and generated it in a linear manner against the time. A H_2O_2 generating activity increased from early to mid-lactation and decreases at the end of lactation. The activity in mastitis milk was lower than that in normal milk. These results suggest that the H_2O_2 generating substance plays an important role for the activation of the LPO-system which is a potent antibacterial system formed by LPO, H_2O_2, and thiocyanate. Less