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The LacLM β-galactosidase of Lactobacillus fermentum K4 is encoded by 2 consecutive genes, lacL (large subunit) and lacM (small subunit), that share 17 overlapping nucleotides. Phylogenetic analysis revealed that this enzyme was closely related to other Lactobacillus β-galactosidases and provided significant insight into its common and distinct characteristics. We cloned both the lacL and lacM genes of L. fermentum K4 and heterologously expressed each in Escherichia coli, although the recombinant enzyme was only functional when both were expressed on the same plasmid. We evaluated the enzymatic properties of this species-specific LacLM β-galactosidase and discovered that it acts as both a hydrolase, bioconverting lactose into glucose and galactose, and a transgalactosylase, generating prebiotic galacto-oligosaccharides (GOS). The recombinant β-galactosidase showed a broad pH optimum and stability around neutral pH. The optimal temperature and Michaelis constant (Km) for the substrates o-nitrophenyl-β-d-galactopyranoside and lactose were, respectively, 40° and 45 to 50°C and 1.31 mM and 27 mM. The enzyme activity was stimulated by some cations such as Na+, K+, and Mg . In addition, activity was also enhanced by ethanol (15%, wt/vol). The transgalactosylation activity of L. fermentum K4 β-galactosidase effectively and rapidly generated GOS, up to 37% of the total sugars from the reaction. Collectively, our results suggested that the β-galactosidase from L. fermentum K4 could be exploited for the formation of GOS. [ABSTRACT FROM AUTHOR]

Objective: To explore the value of shear wave elastography(SWE)stiff rim sign and SWE stiff rim sign combined with BI-RADS classification in qualitative diagnosis and multiple SWE parameters in quantitative diagnosis of benign and malignant breast masses. Methods: One hundred and eighty-eight patients, 18-83 (44±14) years old, with 199 breast masses (maximum diameter, 0.4-5.0 (2.1±1.0) cm) by ultrasound were selected.Qualitative diagnosis was made by SWE stiff rim sign, and SWEmax, SWEmean, SWEmin, SWE1max, SWE2max, SWE3max, SWE1mean, SWE2mean, SWE3mean were obtained. The ROC of each quantitative parameter was drawn, then the AUC was calculated. Results: There were 75 malignant masses and 124 benign masses in 199 breast masses confirmed by pathology. Qualitative diagnosis of BI-RADS classification (χ(2)=155.181) and of SWE stiff rim sign (χ(2)=117.304)and quantitative diagnosis of SWEmax, SWEmean ( t= 6.869,6.305), SWE1max, SWE2max, SWE3max ( t= 8.768,9.059,9.180), SWE1mean, SWE2mean, SWE3mean ( t= 10.041,10.312,10.576) were all statistically significant (all P< 0.01). But there was no statistically significance in quantitative diagnosis of SWEmin ( P> 0.05). The AUC value of qualitative diagnosis of SWE stiff rim sign combined with BI-RADS classification was 0.967, and the sensitivity was 92.0%.For BI-RADS 4a masses,the positive rate of puncture could be increased from 15.3% to 77.8% by combination of SWE hard ring sign. Conclusions: Qualitative diagnosis of SWE stiff rim sign and quantitative diagnosis of multiple SWE parameters are of high accuracy in differentiating benign or malignant breast masses. The combination of SWE stiff rim sign and BI-RADS classification could further improve the sensitivity of qualitative diagnosis, and increase the positive rate of puncture for 4a masses.