TMBP

Lytic polysaccharide monooxygenases (LPMOs) catalyze the oxidative cleavage of glycosidic bonds in industrially important polysaccharides like cellulose.The activity of these monocopper enzymes depends on the presence of H2O2 cosubstrate and reductant.Besides the polysaccharide peroxygenase reaction, LPMOs catalyze reductant oxidase and peroxidase side reactions.The multiplicity and interplay between different LPMO reactions hamper the interpretation of the kinetic data, which is best reflected by the scarcity of the studies of the pH dependency of the LPMO catalysis.Here, we studied the pH dependency of the reductant oxidase/peroxidase as well as the cellulose peroxygenase reactions of TrAA9A, an LPMO from the fungus Trichoderma reesei.The pH dependency of reductant oxidase/peroxidase reaction was governed by the rate-limiting step (reduction of LPMO-Cu(II) or reoxidation of LPMO-Cu(I)) depending on the exptl. conditions.The pH dependency of the kcat and Km(H2O2) of the cellulose peroxygenase reaction was best described by the single base catalysis with pKa around 3.5-4.0.Experiments made in D2O showed isotope effects but only at pD values below 5.0.The conserved second coordination sphere histidine (His163) is the most probable candidate responsible for shaping the pH dependency of the TrAA9A peroxygenase reaction.We propose that the double protonation of His163 at acidic pH alters its conformation to the catalytically incompetent one.However, the little pH dependency of the kcat/Km(H2O2) of the cellulose peroxygenase reaction suggests that at very low H2O2 concentrations, TrAA9A may be efficient catalyst also in the acidic conditions that prevail in fungal habitats.

Harmless treatment of heavy metal-accumulating plants is significant for further development and application of phytoremediation for contaminated soil remediation.In this study, hydrothermal liquefaction (HTL) of low heavy metal-accumulating plants (Jute, Solanum nigrum, and Sorghum) was conducted at different temperatures (280-360°C) for bio-oil productionAttapulgite and Co/Attapulgite were prepared and tested in HTL process.The maximum bio-oil yield and higher heating value (HHV) was found to be 32.04% and 29.61 MJ/kg from HTL of Solanum nigrum with Co/Attapulgite at 300°C.The improvement in quality of bio-oil was marked with decreased O/C content (0.26) and newly formed hydrocarbon fraction with the content of 6.24% with Co/Attapulgite catalyst.It was beneficial for immobilization of Mn, Zn and Cr in hydrochar with addition of catalyst.Notably, Mn and Cd were not detected in any bio-oil, and the proportion of Cr in the bio-oil obtained at 360°C decreased to zero with Co/Attapulgite.XPS and XRD anal. indicated that Mn and Zn existed in the form of Mn3O4, Mn, ZnO and Zn(OH)2 in hydrochar.Finally, potential pathway of heavy metals migration-transformation behaviors during HTL was proposed.