Insights into the catalytic mechanism of a type I sulfide quinone oxidoreductase(SQR)from Acidithiobacillus caldus

Acidithiobacillus caldus,a typical sulfur oxidizer,derives the majority of its energy from sulfur oxidation.And the essential enzyme for sulfide oxidation catalysis is sulfide quinone oxidoreductase(SQR),an ancient flavoprotein.Here,the catalytic mechanism of SQR generated from A.caldus was investigated(SQR^(Ac)).According to phylogenetic study,SQR^(Ac)(ACAty RS11315)is closely related to SQR(BAD99305)of Acidithiobacillus ferrooxidans NASF-1 and is classified as a type I Sqr enzyme.SQR^(Ac)heterologously produced in Escherichia coli exhibits the distinctive absorption peaks(375,450 nm)of the flavoproteins family of proteins in its absorption spectrum.Utilizing site-directed mutagenesis,the function of conserved cysteines in the catalytic pathway was determined.Based on the sulfide quinone redox reactions in vitro of SQR^(Ac)and variations,Cys160 and Cys356 have been identified as enzyme-active residues.Mutation of another cysteine present in all type I SQRs(Cys128)decreased enzyme activity by 56%,indicating that this residue plays an important but non-essential role in enzyme function.In addition,the binding affinities of SQR^(Ac),the visualization of its 3D structure,and the interaction between receptors and ligands were investigated.Finally,a suitable sulfide quinone redox catalytic mechanism for A.caldus was proposed.

Pressure of Newtonian Fluid Flow through Curved Pipes and Elbows

Under conditions of high temperature and high pressure, the non-uniformity of pressure loads has intensified the stress concentration which impacts the safety of curved pipes and elbows. This paper focuses on the pressure distribution and flow characteristic in a curved 90° bend pipe with circular cross-sections, which are widely used in industrial applications. These flow and pressure characteristics in curved bend pipes have been researched by employing numerical simulation and theoretical analysis. Based on the dimensionless analysis method a formula for the pressure of Newtonian fluid flow through the elbow pipes is deduced. Also the pressure distributions of several elbows with different curvature ratio R/D are obtained by numerical methods. The influence of these non-dimensional parameters such as non-dimensional curvature ratio, Reynolds number and non-dimensional axial angle a and circumferential angle fl on the pressure distribution in elbow pipes is discussed in detail. A number of important results have been achieved. This paper provides theoretical and numerical methods to understand the mechanical property of fluid flow in elbow pipes, to analyze the stress and to design the wall thickness of elbow pipes.

Pharmacokinetic interactions between the potential COVID-19 treatment drugs lopinavir/ritonavir and arbidol in rats

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-Co V-2) has occasioned worldwide alarm. Globally, the number of reported confirmed cases has exceeded 84.3 million as of this writing(January 2, 2021). Since there are no targeted therapies for COVID-19。