Improvement of activity and stability of chloroperoxidase by chemical modification

<p>Abstract</p> <p>Background</p> <p>Enzymes show relative instability in solvents or at elevated temperature and lower activity in organic solvent than in water. These limit the industrial applications of enzymes.</p> <p>Results</p> <p>In order to improve the activity and stability of chloroperoxidase, chloroperoxidase was modified by citraconic anhydride, maleic anhydride or phthalic anhydride. The catalytic activities, thermostabilities and organic solvent tolerances of native and modified enzymes were compared. In aqueous buffer, modified chloroperoxidases showed similar <it>K</it>_mvalues and greater catalytic efficiencies <it>k</it>_cat/<it>K</it>_mfor both sulfoxidation and oxidation of phenol compared to native chloroperoxidase. Of these modified chloroperoxidases, citraconic anhydride-modified chloroperoxidase showed the greatest catalytic efficiency in aqueous buffer. These modifications of chloroperoxidase increased their catalytic efficiencies for sulfoxidation by 12%~26% and catalytic efficiencies for phenol oxidation by 7%~53% in aqueous buffer. However, in organic solvent (DMF), modified chloroperoxidases had lower <it>K</it>_mvalues and higher catalytic efficiencies <it>k</it>_cat/<it>K</it>_mthan native chloroperoxidase. These modifications also improved their thermostabilities by 1~2-fold and solvent tolerances of DMF. CD studies show that these modifications did not change the secondary structure of chloroperoxidase. Fluorescence spectra proved that these modifications changed the environment of tryptophan.</p> <p>Conclusion</p> <p>Chemical modification of epsilon-amino groups of lysine residues of chloroperoxidase using citraconic anhydride, maleic anhydride or phthalic anhydride is a simple and powerful method to enhance catalytic properties of enzyme. The improvements of the activity and stability of chloroperoxidase are related to side chain reorientations of aromatics upon both modifications.</p

Green's functions of multiband non-Hermitian systems

Green's functions of non-Hermitian systems play a fundamental role in various dynamical processes. Because non-Hermitian systems are sensitive to boundary conditions due to the non-Hermitian skin effect, open-boundary Green's functions are closely related to the non-Bloch band theory. While the exact formula of open-boundary Green's functions in single-band non-Hermitian systems proves to be an integral along the generalized Brillouin zone (GBZ), the proper generalization in generic multiband systems remains unclear. In this work, we derive a formula of open-boundary Green's functions in multiband non-Hermitian systems by viewing the multiband GBZ on the Riemann surface. This formula can be applied to describe directional amplification in multiband systems, which can be verified at various experimental platforms.Comment: 7 pages, 4 figure

Danshensu exerts cardioprotective effects in rats with acute myocardial infarction via reduction of infiltration of inflammatory cells and mitigation of myocardial fibrosis

Purpose: To investigate the mitigative impact of danshensu on heart tissues in acute myocardial infarction (AMI) rats, and the mechanism of action involved. Methods: Seventy-five male Sprague-Dawley (SD) rats were used in this study. After successful induction of myocardial infarction, the rats were divided into model group (MG), low-dose danshensu group (LDG; 15 mg/kg), middle-dose danshensu group (MDG; 30 mg/kg), and high-dose danshensu group (HDG; 60 mg/kg), with 15 rats per group. Rats in sham group (SG; n = 15) served as control. Serum levels of biochemical indicators and expressions of various proteins in myocardial tissue were determined using Western blotting, and compared amongst the rat groups. Results: Serum cTnI concentrations in MDG and HDG were significantly decreased, relative to the corresponding concentrations in MDG. There were significantly lower serum concentrations of IL-1 in MDG and HDG than in model rats. Rats in HDG had lower serum IL-6 concentration than MG rats, while TNF-α levels were down-regulated in MDG and HDG, relative to MG (p &lt; 0.05). Conclusion: Danshensu protects the heart function of rats with AMI by decreasing inflammationderived cells and mitigating myocardial fibrosis. Thus, it may be useful in the management of AMI in humans but clinical trials are necessary to ascertain this. Keywords: Danshens; Acute myocardial infarction; Myocardial ischemia-reperfusion; Myocardial fibrosi

Quaternary amines exert anti-myocardial ischemia effects via regulation of energy metabolism and oxygen free radicals in myocardial cells in acute myocardial infarction rats

Purpose: To investigate the effect of quaternary amines on myocardial cells of a rat model of cardiac arrest, with respect to energy generation potential and oxygen free radicals. Methods: Forty-five Sprague-Dawley (SD) rats were assigned to sham, model and quaternary amine groups (each with 15 rats). After their corresponding treatments, lectrocardiogram (ECG) monitoring of the rats in the three groups at various time periods was carried out. Serum levels of myocardial enzymes, thromboxane B2 (TXB2), prostacyclin I2 (PGI2), serum carbon monoxide (CO), and changes in endothelial carbon monoxide synthase (eNOS) and endothelin (ET), were determined. Results: The levels of NO and eNOS were significantly reduced in model rats, relative to sham operation rats, while ET was significantly elevated in sham rats (p &lt; 0.05). There were higher levels of NO and eNOS in the quaternary amine group than in model rats, but ET was higher in quaternary amine group than in model rats. Thromboxane B2 (TXB2) concentration was higher in model rats than in sham rats (p &lt; 0.05). While PGI2 was markedly lower in quaternary group than in sham operation rats. TXB2 was lower in the quaternary amine group than in model rats, while PGI2 was significantly higher in quaternary amine group, relative to model rats (p &lt; 0.05). Conclusion: Quaternary amines exert anti-myocardial effects by regulating energy metabolism and oxygen free radicals in myocardial cells of congestive heart failure rats, and thus are potentially useful for the management of acute myocardial infarction. Keywords: Quaternary amine; Acute myocardial infarction; Electrocardiogram; Serum myocardial enzymes; Myocardial cell

Geometric Origin of Non-Bloch PT Symmetry Breaking

The parity-time (PT) symmetry of a non-Hermitian Hamiltonian leads to real (complex) energy spectrum when the non-Hermiticity is below (above) a threshold. Recently, it has been demonstrated that the non-Hermitian skin effect generates a new type of PT symmetry, dubbed the non-Bloch PT symmetry, featuring unique properties such as high sensitivity to the boundary condition. Despite its relevance to a wide range of non-Hermitian lattice systems, a general theory is still lacking for this generic phenomenon even in one spatial dimension. Here, we uncover the geometric mechanism of non-Bloch PT symmetry and its breaking. We find that non-Bloch PT symmetry breaking occurs by the formation of cusps in the generalized Brillouin zone (GBZ). Based on this geometric understanding, we propose an exact formula that efficiently determines the breaking threshold. Moreover, we predict a new type of spectral singularities associated with the symmetry breaking, dubbed non-Bloch van Hove singularity, whose physical mechanism fundamentally differs from their Hermitian counterparts. This singularity is experimentally observable in linear responses.Comment: 19 pages,11 figures, including supplemental materia

Steady-state edge burst: From free-particle systems to interaction-induced phenomena

The interplay between the non-Hermitian skin effect and the imaginary gap of lossy lattices results in the edge burst, a boundary-induced dynamical phenomenon in which an exceptionally large portion of particle loss occurs at the edge. Here, we find that this intriguing non-Hermitian dynamical phenomenon can be exactly mapped into the steady-state density distribution of a corresponding open quantum system. Consequently, the bulk-edge scaling relation of loss probability in the edge burst maps to that of steady-state density. Furthermore, we introduce a many-body open-system model in which the two-body loss generates an interaction-induced non-Hermitian skin effect. Using the positive-$P$ method, we demonstrate the validity of the scaling relation for steady-state correlators. These results provide a unique perspective on the interaction-induced many-body non-Hermitian skin effect. Our predictions are testable in state-of-the-art experimental platforms.Comment: 13 pages, 6 figure