Adsorption properties of BSA and DsRed proteins deposited on thin SiO2 layers: optically non-absorbing versus absorbing proteins.

Protein adsorption on solid surfaces is of interest for many industrial and biomedical applications, where it represents the conditioning step for micro-organism adhesion and biofilm formation. To understand the driving forces of such an interaction we focus in this paper on the investigation of the adsorption of bovine serum albumin (BSA) (optically non-absorbing, model protein) and DsRed (optically absorbing, naturally fluorescent protein) on silica surfaces. Specifically, we propose synthesis of thin protein layers by means of dip coating of the dielectric surface in protein solutions with different concentrations (0.01-5.0 g l-1). We employed spectroscopic ellipsometry as the most suitable and non-destructive technique for evaluation of the protein layers' thickness and optical properties (refractive index and extinction coefficient) after dehydration, using two different optical models, Cauchy for BSA and Lorentz for DsRed. We demonstrate that the thickness, the optical properties and the wettability of the thin protein layers can be finely controlled by proper tuning of the protein concentration in the solution. These results are correlated with the thin layer morphology, investigated by AFM, FTIR and PL analyses. It is shown that the proteins do not undergo denaturation after dehydration on the silica surface. The proteins arrange themselves in a lace-like network for BSA and in a rod-like structure for DsRed to form mono- and multi-layers, due to different mechanisms driving the organization stage.

Expression of pyrrothine N-acyltransferase activities in Saccharothrix algeriensis NRRL B-24137: new insights into dithiolopyrrolone antibiotic biosynthetic pathway.

AIMS: The hypothetical dithiolopyrrolone biosynthetic pathway includes a final step of pyrrothine nucleus acylation. The presence of an enzymatic activity catalysing this reaction was investigated in Saccharothrix algeriensis NRRL B-24137. To understand the effect exerted by organic acids on the level of dithiolopyrrolone production, their influence on enzymatic expression was studied. METHODS AND RESULTS: The transfer of acetyl-CoA or benzoyl-CoA on pyrrothine was assayed in the cell-free extract of Sa. algeriensis NRRL B-24137. This study reports the presence of an enzymatic activity catalysing this reaction that was identified as either pyrrothine N-acetyltransferase or N-benzoyltransferase. The stimulation of benzoyl-pyrrothine (BEP) production by addition of benzoic acid at 1.25 mmol l(-1) into the culture medium was demonstrated, and results showed that under the same conditions of growth, pyrrothine N-benzoyltransferase specific activity was doubled. CONCLUSIONS: This study shows that BEP production is enhanced in the presence of benzoic acid partly because of an induction of pyrrothine N-benzoyltransferase. SIGNIFICANCE AND IMPACT OF THE STUDY: The antitumor and antibiotic properties of dithiolopyrrolones are related to their variable acyl groups. New insights into regulation of biosynthetic pathway, especially the step of pyrrothine acylation, could lead after further studies to yield improvement and to selective production of dithiolopyrrolones with new biological activities.

Blood schizontocidal activity of methylene blue in combination with antimalarials against Plasmodium falciparum.

Methylene blue (MB) is the oldest synthetic antimalarial. It is not used anymore as antimalarial but should be reconsidered. For this purpose we have measured its impact on both chloroquine sensitive and resistant Plasmodium strains. We showed that around 5 nM of MB were able to inhibit 50% of the parasite growth in vitro and that late rings and early trophozoites were the most sensitive stages; while early rings, late trophozoites and schizonts were less sensitive. Drug interaction study following fractional inhibitory concentrations (FIC) method showed antagonism with amodiaquine, atovaquone, doxycycline, pyrimethamine; additivity with artemether, chloroquine, mefloquine, primaquine and synergy with quinine. These results confirmed the interest of MB that could be integrated in a new low cost antimalarial combination therapy.

Effect of prolonged treatment with tyramine on glucose tolerance in streptozotocin-induced diabetic rats.

The biogenic amine tyramine has been reported to stimulate in vitro glucose transport in adipocytes, cardiomyocytes and skeletal muscle, and to improve in vivo glucose utilization in rats. These effects were dependent on amine oxidation, since they were blocked by inhibitors of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO). We thus tested in this work whether a prolonged treatment with tyramine could improve glucose tolerance in streptozotocin-induced diabetic rats. First, tyramine content of standard rodent chow was determined by HPLC and daily tyramine intake of control rats was estimated to be around 26 micromol/kg body weight. Then, tyramine was administred during 3 weeks in streptozotocin-induced diabetic rats at 29 micromol/kg by daily i.p. injection alone or together with vanadate 0.02 micromol/kg. In another group of diabetic rats, tyramine was subcutaneously delivered at 116 micromol/kg/day by osmotic minipumps. All tyramine treatments resulted in a decrease of the hyperglycemic responses to an i.p. glucose load. Adipocytes isolated from either untreated or treated diabetic rats were sensitive to the stimulation of glucose uptake by tyramine. However, diabetic animals receiving tyramine for three weeks did not recover from their hyperglycemia, hypoinsulinemia and glucosuria. These results show that the improvement of glucose tolerance induced by prolonged tyramine administration occurs in an insulin-depleted model and probably results from peripheral insulin-like actions of the oxidation of MAO/SSAO substrates, such as the stimulation of glucose uptake into adipocytes.