FLAVIN-SENSITIZED PHOTODYNAMIC MODIFICATION OF MULTISUBUNIT PROTEINS

Abstract— Riboflavin 5'-phosphate (FMN)-sensitized photodynamic modifications of multisubunit alcohol dchydrogenase, bacterial luciferase. L-glutamate dehydrogenase, and catalase all lead to significant formation of crosslinked species. On the contrary, irradiation of monomeric lysozyme, trypsin inhibitor, trypsin, and bovine serum albumin in the presence of FMN yields either no or only trace amounts of polymerized molecules. Photodynamic modifications thus appear to be much more efficient in crosslinking proteins with quaternary structures in their native forms. While no photodegradations of other proteins were found, FMN-sensitized modifications of the nonidentical dimeric (αß) bacterial luciferase resulted in the formation of two degraded fragments as well as two polymerized species. Singlet oxygen is shown to be involved in the photopolymerization of luciferase but it is unclear whether singlet oxygen is the sole species active in initiating the crosslinking reaction(s). FMN also sensitizes effective inactivations of luciferase which can be attributed to actions of singlet oxygen, triplet FMN, H₂O₂. and superoxide anion. Photodynamic inactivation of luciferase proceeds faster than photopolymerization; these processes are thus not coupled.     

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Delivery of Methylene Blue and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate from cross-linked poly(vinyl alcohol) hydrogels: A potential means of photodynamic therapy of infected wounds

Poly(vinyl alcohol)–borate complexes were evaluated as a potentially novel drug delivery platform suitable for in vivo use in photodynamic antimicrobial chemotherapy (PACT) of wound infections. An optimised formulation (8.0% w/w PVA, 2.0% w/w borax) was loaded with 1.0 mg ml⁻¹ of the photosensitisers Methylene Blue (MB) and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP). Both drugs were released to yield receiver compartment concentrations (>5.0 μg ml⁻¹) found to be phototoxic to both planktonic and biofilm-grown methicillin-resistant Staphylococcus aureus (MRSA), a common cause of wound infections in hospitals. Newborn calf serum, used to simulate the conditions prevalent in an exuding wound, did not adversely affect the properties of the hydrogels and had no significant effect on the rate of TMP-mediated photodynamic kill of MRSA, despite appreciably reducing the fluence rate of incident light. However, MB-mediated photodynamic kill of MRSA was significantly reduced in the presence of calf serum and when the clinical isolate was grown in a biofilm. Results support the contention that delivery of MB or TMP using gel-type vehicles as part of PACT could make a contribution to the photodynamic eradication of MRSA from infected wounds.     

Modulation of surface charge, particle size and morphological properties of chitosan-TPP nanoparticles intended for gene delivery

This work investigates the polyanion initiated gelation process in fabricating chitosan-TPP (tripolyphosphate) nanoparticles in the size range of 100-250 nm intended to be used as carriers for the delivery of gene or protein macromolecules. It demonstrates that ionic gelation of cationic chitosan molecules offers a flexible and easily controllable process for systematically and predictably manipulating particle size and surface charge which are important properties in determining gene transfection efficacy if the nanoparticles are used as non-viral vectors for gene delivery, or as delivery carriers for protein molecules. Variations in chitosan molecular weight, chitosan concentration, chitosan to TPP weight ratio and solution pH value were examined systematically for their effects on nanoparticle size, intensity of surface charge, and tendency of particle aggregation so as to enable speedy fabrication of chitosan nanoparticles with predetermined properties. The chitosan-TPP nanoparticles exhibited a high positive surface charge across a wide pH range, and the isoelectric point (IEP) of the nanoparticles was found to be at pH 9.0. Detailed imaging analysis of the particle morphology revealed that the nanoparticles possess typical shapes of polyhedrons (e.g., pentagon and hexagon), indicating a similar crystallisation mechanism during the particle formation and growth process. This study demonstrates that systematic design and modulation of the surface charge and particle size of chitosan-TPP nanoparticles can be readily achieved with the right control of critical processing parameters, especially the chitosan to TPP weight ratio.     

Residually nilpotent one-relator groups with nontrivial centre

We determine explicitly the residually nilpotent one-relator groups with nontrivial centre. We show also that, if is a one-relator group, then is residually nilpotent if, and only if, its central quotient is residually nilpotent.