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991.
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QI ZHOU JICHENG WANG ZHUANG GUO LIYA YAN QING ZHANG WEI CHEN XIAO-MING LIU HE-PING ZHANG 《International Journal of Dairy Technology》2009,62(2):249-254
The fermentation characteristics of Lactobacillus casei Zhang in mare milk and transit tolerance during refrigerated storage for 28 days were evaluated. There were no dramatic changes in the viable counts of L. casei Zhang in the fermented mare milk samples during storage at various inoculation levels. L. casei Zhang showed good tolerance to the simulated transit juice and maintained high viability in mare milk (above 108 cfu/g) during storage. Our results showed that L. casei Zhang had good probiotic properties, and suggest that mare milk could serve as the vehicle for the delivery of L. casei Zhang. 相似文献
994.
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°C 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 Mg2+. 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. 相似文献
995.
The rabbit platelet metabolizes platelet-activating factor (PAF) intracellulary. PAF is deacetylated to produce lysoPAF which,
in turn, can be acylated to produce 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl GPC). Some PAF receptor antagonists have been shown to inhibit this metabolic conversion.
In the present study we examined whether the PAF receptor antagonists SRI 63-441 and WEB 2086 would inhibit the metabolism
of PAF by intact rabbit platelets. In addition, we examined whether iloprost, a stable analogue of prostaglandin I2 (PGI2), and a potent inhibitor of platelet activation induced by a range of agonists, would also inhibit PAF metabolism. We found
that SRI 63-441 and WEB 2086 caused an almost complete inhibition of the conversion of PAF to alkylacyl GPC. Iloprost caused
up to a 50% inhibition of PAF metabolism compared to antagonist-free controls. Iloprost (and PGI2) is thought to inhibit platelet response by elevation of cAMP, while receptor antagonists act by blocking PAF binding to
its receptor. Since iloprost caused partial inhibition of PAF metabolism, the results of this study suggest that inhibition
of PAF metabolism does not occur solely due to competitive inhibition of PAF binding to its receptor.
Based on a paper presented at the Third International Conference on Platelet Activating Factor and Structurally Related Alkyl
Ether Lipids, Tokyo, Japan, May 1989. 相似文献
996.
997.
998.
Nanometric cutting involves materials removal and deformation evolution in the surface at nanometer scale. At this length
scale, atomistic simulation is a very useful tool to study the cutting process. In this study, large-scale molecular dynamics
(MD) simulations with the model size up to 10 millions atoms have been performed to study three-dimensional nanometric cutting
of copper. The EAM potential and Morse potential are used, respectively, to compute the interaction between workpiece atoms
and the interactions between workpiece atoms and tool atoms. The material behavior, surface and subsurface deformation, dislocation
movement, and cutting forces during the cutting processes are studied. We show that the MD simulation model of nanometric
cutting has to be large enough to eliminate the boundary effect. Moreover, the cutting speed and the cutting depth have to
be considered in determining a suitable model size for the MD simulations. We have observed that the nanometric cutting process
is accompanied with complex material deformation, dislocation formation, and movement. We find that as the cutting depth decreases,
the tangential cutting force decreases faster than the normal cutting force. The simulation results reveal that as the cutting
depth decreases, the specific cutting force increases, i.e., “size effect” exists in nanometric cutting. 相似文献
999.
1000.