Tail-associated structural protein gp61 of Staphylococcus aureus phage φMR11 has bifunctional lytic activity

A tailed bacteriophage, φMR11 (siphovirus), was selected as a candidate therapeutic phage against Staphylococcus aureus infections. Gene 61, one of the 67 ORFs identified, is located in the morphogenic module. The gene product (gp61) has lytic domains homologous to CHAP (corresponding to an amidase function) at its N-terminus and lysozyme subfamily 2 (LYZ2) at its C-terminus. Each domain of gp61 was purified as a recombinant protein. Both the amidase [amino acids (aa) 1–150] and the lysozyme (aa 401–624) domains but not the linker domain (aa 151–400) caused efficient lysis of S . aureus . Immunoelectron microscopy localized gp61 to the tail tip of the φMR11 phage. These data strongly suggest that gp61 is a tail-associated lytic factor involved in local cell-wall degradation, allowing the subsequent injection of φMR11 DNA into the host cytoplasm. Staphylococcus aureus lysogenized with φMR11 was also lysed by both proteins. Staphylococcus aureus strains on which φMR11 phage can only produce spots but not plaques were also lysed by each protein, indicating that gp61 may be involved in 'lysis from without'. This is the first report of the presence of a tail-associated virion protein that acts as a lysin, in an S. aureus phage.     

Towards the mechanism and comparative effect of diphenyl diselenide, diphenyl ditelluride and ebselen under various pathophysiological conditions in rat's kidney preparation

As an extension of our previous work we not only evaluated the relationship between acidosis and lipid peroxidation in rat's kidney homogenate, but also determined for the first time the potential anti-oxidant activity of diphenyl diselenide, diphenyl ditelluride and ebselen at a range of pH values (7.4–5.4). Because of the pH dependency of iron redox cycling, pH and iron need to be well controlled and for the reason we tested a number of pH values (from 7.4 to 5.4) to get a closer idea about the role of iron under various pathological conditions. Acidosis increased rate of lipid peroxidation in the absence Fe (II) in kidney homogenates especially at pH 5.4. This higher extent of lipid peroxidation can be explained by; the mobilized iron which may come from reserves where it is weakly bound. Addition of iron (Fe) chelator desferoxamine (DFO) to reaction medium completely inhibited the peroxidation processes at all studied pH values including acidic values (5.8–5.4). In the presence of Fe (II) acidosis also enhanced detrimental effect of Fe (II) especially at pH (6.4–5.4). Diphenyl diselenide significantly protected lipid peroxidation at all studied pH values, while ebselen offered only a small statistically non-significant protection. The highest anti-oxidant potency was observed for diphenyl ditelluride. These differences in potencies were explained by the mode of action of these compounds using their catalytic anti-oxidant cycles. However, changing the pH of the reaction medium did not alter the anti-oxidant activity of the tested compounds. This study provides evidence for acidosis catalyzed oxidative stress in kidney homogenate and for the first time anti-oxidant potential of diphenyl diselenide and diphenyl ditelluride not only at physiological pH but also at a range of acidic values.     

Photochemical covalent binding of urocanic acid to polynucleic acids

Photolysis of E-[ring-2-14C]urocanic acid (UA) with native or denatured calf thymus DNA leads to covalent binding of the radiolabel to the nucleic acid. A similar observation is made upon photolysis of the labeled UA with the polyribonucleotides, in which case a strong preference is observed for binding to poly[U]. DNA or poly[U], which had been reacted with UA and purified by dialysis and multiple precipitations, releases UA upon further irradiation with 254 nm light (as expected for cyclobutane adducts). Quantum efficiencies for binding of the UA to native DNA have been measured at 308 and 266 nm and are 0.30 x 10(-5) and 1.3 x 10(-4), respectively, at comparable reactant concentrations. The large increase at the shorter wavelength (where DNA absorption is more competitive) is taken as evidence for the primary role of a DNA excited state in initiating the binding reaction(s).     

Platelet-activating factor secreted by DDAVP-treated monocytes mediates von willebrand factor release from endothelial cells

We have previously shown that although DDAVP (1-deamino-8-D-arginine vasopressin), a synthetic analogue of the natural hormone arginine vasopressin, does not directly promote release of vWf from human umbilical vein endothelial cells (ECs), enhanced release does occur when ECs were exposed to either monocytes or to supernatants recovered from DDAVP-treated monocytes. In the present study, we have found that exposure of monocytes to DDAVP did not increase secretion of interleukins (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF-α), growth factors G-CSF (granulocyte-), GM-CSF (granulocyte, monocyte-colony stimulating factor), prostaglandins (PG) E₂, PGF_2α, or PGI₂ or purine nucleotides such as ATP and ADP. However, increased levels of platelet-activating factor (PAF) were secreted by DDAVP-treated monocytes in a time- and dose-dependent manner that positively correlated with the enhancement in vWf release from ECs. Moreover, this effect could also be elicited when lipid extracts of these supernatants or purified PAF were added directly to ECs. This response could be inhibited with (±)-trans-2,5-Bis(3,4,5-trimethoxyphenyl)-1,3-dioxolane, a specific PAF receptor antagonist, when the ECs were exposed to supernatants from DDAVP-treated monocytes or to pure PAF. The present data indicate that enhanced secretion of PAF from monocytes is one mechanism whereby DDAVP can provoke release of vWf from ECs. © 1993 Wiley-Liss, Inc.     

Macrophylloside, a flavone glucoside from Primula macrophylla

A new flavone glucoside macrophylloside has been isolated from the whole plant of Primula macrophylla and its structure was determined by spectroscopic methods as 2′-hydroxy-7-O-β- -glucopyranosyloxyflavone. Sitosterol glucoside was also isolated for the first time from this plant.