Oxidation of Benzyl Alcohol with CuII and ZnII Complexes of the Phenoxyl Radical as a Model of the Reaction of Galactose Oxidase

Profound insights into the catalytic mechanism of galactose oxidase (GO) are offered by new models of the active form of the metalloenzyme. The important role of the Cu^II center in the oxidation of benzyl alcohol to benzaldehyde by the Cu^II–phenoxyl radical complex of ligand 1 has been revealed by comparison with the reactivity of the corresponding Zn^II–phenoxyl radical complex; py=2-pyridyl.     

Antistatic PVC-graphene Composite through Plasticizer-mediated Exfoliation of Graphite

Multilayer graphene was prepared by mechanical exfoliation of natural graphite with dioctyl phthalate(DOP) as milling medium without solvent. The obtained mixture could be directly mixed with poly(vinyl chloride)(PVC) for melt-forming, with DOP acting as plasticizer and graphene acting as conductive filler for antistatic performance. The composite showed surface resistance of 2.5 ×10~6 Ω/□ at 1 wt% carbon additive, significantly lower than approx. 7 wt% of raw graphite required for achieving the same level. This value is low enough for practical antistatic criterion of 3 × 10~8 Ω/□. The effect of filler addition on mechanical performance was minimal, or even beneficial for the milled carbon in contrast to the case of raw graphite.     

Cloning and characterization of the gene cluster encoding arthrofactin synthetase from Pseudomonas sp. MIS38

Arthrofactin is a potent cyclic lipopeptide-type biosurfactant produced by Pseudomonas sp. MIS38. In this work, an arthrofactin synthetase gene cluster (arf) spanning 38.7 kb was cloned and characterized. Three genes termed arfA, arfB, and arfC encode ArfA, ArfB, and ArfC, containing two, four, and five functional modules, respectively. Each module bears condensation, adenylation, and thiolation domains, like other nonribosomal peptide synthetases. However, unlike most of them, none of the 11 modules possess the epimerization domain responsible for the conversion of amino acid residues from L to D form. Possible L- and D-Leu adenylation domains specifically recognized only L-Leu. Moreover, two thioesterase domains are tandemly located at the C-terminal end of ArfC. These results suggest that ArfA, ArfB, and ArfC assemble to form a unique structure. Gene disruption of arfB impaired arthrofactin production, reduced swarming activity, and enhanced biofilm formation.     

Uniform boundedness of the solutions for a one-dimensional isentropic model system of compressible viscous gas

This paper studies an initial boundary value problem for a one-dimensional isentropic model system of compressible viscous gas with large external forces, represented by v _t –u _x =0,u _t +(av ^–) _x =(u _x /v) _x +f( ₀ ^x vdx,t), with (v(x, 0),u(x, 0))= (v ₀(x),u ₀(x)),u(0,t)=u(1,t)=0. Especially, the uniform boundedness of the solution in time is investigated. It is proved that for arbitrary large initial data and external forces, the problem uniquely has an uniformly bounded, global-in-time solution with also uniformly positive mass density, provided the adiabatic constant (>1) is suitably close to 1. The proof is based on L ²-energy estimates and a technique used in [9].     

Rotation sets of surface homeomorphisms

We consider the rotation setR of a homeomorphismf, isotopic to the identity, of a closed surface of genusg2. We show if Int(R) is nonempty and contains an element which is realized by an asymptotic measure, then all the rational points of Int(R) are realized by periodic orbits. We raise an example to show that the second condition above is indispensable ifg2. We also show that ifR contains a (g+1)-simplex whose vertices are realizable by periodic orbits, then the topological entropy off is positive.     

Chemoenzymatic synthesis of glycopeptides with PglB, a bacterial oligosaccharyl transferase from Campylobacter jejuni

The gram-negative bacterium Campylobacter jejuni has a general N-linked glycosylation pathway encoded by the pgl gene cluster. One of the proteins in this cluster, PgIB, is thought to be the oligosaccharyl transferase due to its significant homology to Stt3p, a subunit of the yeast oligosaccharyl transferase complex. PgIB has been shown to be involved in catalyzing the transfer of an undecaprenyl-linked heptasaccharide to the asparagine side chain of proteins at the Asn-X-Ser/Thr motif. Using a synthetic disaccharide glycan donor (GaINAc-alpha1,3-bacillosamine-pyrophosphate-undecaprenyl) and a peptide acceptor substrate (KDFNVSKA), we can observe the oligosaccharyl transferase activity of PgIB in vitro. Furthermore, the preparation of additional undecaprenyl-linked glycan variants reveals the ability of PgIB to transfer a wide variety of saccharides. With the demonstration of PgIB activity in vitro, fundamental questions surrounding the mechanism of N-linked glycosylation can now be addressed.