Byproducts and proposed reaction pathways for the combined UV/H₂O₂ degradation of the conjugated carbon double bonds of Adda side chain of MCLR.

<p>Byproducts and proposed reaction pathways for the combined UV/H₂O₂ degradation of the conjugated carbon double bonds of Adda side chain of MCLR.</p

Top-ranking features useful for protein binding hot spot prediction by random forest.

<p>‘%IncMSE’ indicates the increase of the mean standard error (MSE) after the permutation of the features. The definitions of the top 25 important features are listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.t005" target="_blank">Table 5</a>.</p

Mechanism and Reaction Pathways for Microcystin-LR Degradation through UV/H₂O₂ Treatment

<div><p>Microcystin-LR (MCLR) is the most common cyanotoxin in contaminated aquatic systems. MCLR inhibits protein phosphatases 1 and 2A, leading to liver damage and tumor formation. MCLR is relatively stable owing to its cyclic structures. The combined UV/H₂O₂ technology can degrade MCLR efficiently. The second-order rate constant of the reaction between MCLR and hydroxyl radical (·OH) is 2.79(±0.23)×10¹⁰ M⁻¹ s⁻¹ based on the competition kinetics model using nitrobenzene as reference compound. The probable degradation pathway was analyzed through liquid chromatography mass spectrometry. Results suggested that the major destruction pathways of MCLR were initiated by ·OH attack on the benzene ring and diene of the Adda side chain. The corresponding aldehyde or ketone peptide residues were formed through further oxidation. Another minor destruction pathway involved ·OH attack on the methoxy group of the Adda side chain, followed by complete removal of the methoxy group. The combined UV/H₂O₂ system is a promising technology for MCLR removal in contaminated aquatic systems.</p></div

The distribution of Bdifr for the fourth amino acid group (in (a)), and for the third group (in (b)), and for the first and second groups (in (d)), and the distribution of Bavgr for the third group (in (c)).

<p>The y-axes denote ΔΔ<i>G</i>. ∘: ILE, VAL, LEU, MET, ALA and GLY; ◻: CYS, THR, SER, PRO, HIS, GLN and ASN; ♢: GLU, ASP, LYS and ARG; ▿: PHE, TRP and TYR. The importance of V10, V8 and V7 is ranked as 9^<i>th</i>, 19^<i>th</i> and 24^<i>th</i>, respectively, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.g002" target="_blank">Fig 2</a>, while the Pearson correlation coefficients of the three features are -0.054, -0.213 and -0.313, respectively, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.t005" target="_blank">Table 5</a>. V4 and V6 are not in the top 40 important features in randomForest.</p

Byproducts and proposed reaction pathways for the combined UV/H₂O₂ degradation of the conjugated carbon double bonds of Adda side chain of MCLR.

<p>Byproducts and proposed reaction pathways for the combined UV/H₂O₂ degradation of the conjugated carbon double bonds of Adda side chain of MCLR.</p

LC-MS chromatograph of MCLR after 45 min of UV/H₂O₂ treatment.

<p>LC-MS chromatograph of MCLR after 45 min of UV/H₂O₂ treatment.</p

Reaction intermediates of MCLR degraded by the combined UV/H₂O₂ treatment.

<p>Reaction intermediates of MCLR degraded by the combined UV/H₂O₂ treatment.</p

Relative yield of product ions versus time in the UV/H2O2 treatment.

<p>Relative yield of product ions versus time in the UV/H2O2 treatment.</p

The distribution of top three features V14 (in (a)), V34 (in (b)) and V84 (in (c)).

<p>The definitions of V14, V34 and V84 are listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.t005" target="_blank">Table 5</a>. The importance of V14, V34 and V84 is ranked as 1^<i>st</i>, 2^<i>nd</i> and 3^<i>rd</i>, respectively, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.g002" target="_blank">Fig 2</a>, while the Pearson correlation coefficients of the three features are -0.315, -0.277 and -0.273, respectively, as shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0144486#pone.0144486.t005" target="_blank">Table 5</a>. The y-axes denote ΔΔ<i>G</i>. ∘: ILE, VAL, LEU, MET, ALA and GLY; ◻: CYS, THR, SER, PRO, HIS, GLN and ASN; ♢: GLU, ASP, LYS and ARG; ▿: PHE, TRP and TYR. (d) shows an example of the neighborhood of the two mutations (in brown): Tyr54 and Tyr55 of Chain A (in red) in 1BXI together with the partner protein (Chain B in green). All carbon atoms in the neighborhood which have no covalent bond with any oxygen or nitrogen are shown in ‘sphere’ view. The alanine mutation of Tyr54 has ΔΔ<i>G</i> = 4.83kcal/mol with the smallest value of V84, and that of Tyr55 has ΔΔ<i>G</i> = 4.63kcal/mol with the smallest value of V34.</p

Parameters determined under different nitrobenzene concentrations.

<p>Parameters determined under different nitrobenzene concentrations.</p