Oxygen dependent pyruvate oxidase expression and production in Streptococcus sanguinis

The objective of this study was to characterize the oxygen dependent regulation of pyruvate oxidase （SpxB） gene expression and protein production in Streptococcus sanguinis （S. sanguinis）. SpxB is responsible for the generation of growth-inhibiting amounts of hydrogen peroxide （H202） able to antagonize cariogenic Strepto- coccus mutans （S. mutans）. Furthermore, the ecological consequence of H202 production was investigated in its self-inhibiting ability towards the producing strain. Expression of spxB was determined with quantitative Real-Time RT-PCR and a fluorescent expression reporter strain. Protein abundance was investigated with FLAG epitope engineered in frame on the C-terminal end of SpxB. Self inhibition was tested with an antagonism plate assay. The expression and protein abundance decreased in cells grown under anaerobic conditions. S. sanguinis was resistant against its own produced H202, while cariogenic S. mutans was inhibited in its growth. The results suggest that S. sanguinis produces H202 as antimicrobial substance to inhibit susceptible niche competing species like S. mutans during initial biofilm formation, when oxygen availability allows for spxB expression and Spx production.

Effects of Used Battery on Key Enzyme Activity during the Germination of Wheat Seeds

[Objective] This study aimed to explore the effects of used battery lixivium on wheat germination. [Method] The wheat seeds were treated with used battery lix- ivium at different concentrations to detect the change of activities of amylase, pro- tease, pyruvate dehydrogenase （PDH） and polyphenol oxidase （PPO） during the ger- mination period. [Result] The results showed that the used battery affected enzyme activity. With the increase of concentration of used battery lixivium, trends of the changes of amylase and protease activities were not different. The activities were en- hanced at low concentrations of lixivium, while were inhibited at high concentrations. The tends of changes of pyruvate dehydrogenase （PDH） and polyphenol oxidase （PPO） activities were not consistent with that of either amylase or protease, which showed continuous downward trends with the increasing concentration of used battery lixivium. [Conclusion] This study is of great practical significance for understanding the effects of used battery lixivium on the germination of wheat seeds.

A nano-functionalized real-time electrochemiluminescent biosensor for alanine transaminase assay

An electrochemiluminescent (ECL) biosensor was constructed for selective assay of alanine aminotransferase (ALT) based on the enzymatically catalyzed oxidation of pyruvate by pyruvate oxidase (PYOD). The composite of potassium ferricyanide and carbon nanotube was adopted to pre-functionalize the basal platinum electrode while the potassium ferricyanide acted as the activator of PYOD. The ALT catalyzed the reaction of L-alanine and-ketoglutarate to produce pyruvate which could be further enzymatically oxidized by PYOD to yield H2O2 to intensify the ECL of luminol. The biosensor showed rapid response for real-time measurement of ALT in the linear concentration range from 0.00475 to 350 U/L (r = 0.993) with a relatively standard deviation of 2.5% (CALT = 47.5 U/L,n = 6). The biosensor was applied to assay the ALT in rat serum with average recovery of 90.5%.