Flavia Forchiassin

Layer-by-Layer Self-Assembled Osmium Polymer-Mediated Laccase Oxygen Cathodes for Biofuel Cells: The Role of Hydrogen Peroxide

High potential purified Trametes trogii laccase has been studied as a biocatalyst for oxygen cathodes composed of layer-by-layer self-assembled thin films by sequential immersion of mercaptopropane sulfonate-modified Au electrode surfaces in solutions containing laccase and osmium-complex bound to poly(allylamine), (PAH-Os). The polycation backbone carries the Os redox relay, and the polyanion is the enzyme adsorbed from a solution of a suitable pH so that the protein carries a net negative charge. Enzyme thin films were characterized by quartz crystal microbalance, ellipsometry, cyclic voltammetry, and oxygen reduction electrocatalysis under variable oxygen partial pressures with a rotating disk electrode. New kinetic evidence relevant to biofuel cells is presented on the detection of traces of H(2)O(2), intermediate in the O(2) reduction, with scanning electrochemical microscopy (SECM). Furthermore the inhibitory effect of peroxide on the biocatalytic current resulted in abnormal current dependence on the O(2) partial pressure and peak shape with hysteresis in the polarization curves under stagnant conditions, which is offset upon stirring with the RDE. The new kinetic evidence reported in the present work is very relevant for the operation of biofuel cells under stagnant conditions of O(2) mass transport.

The effect of light and cyclic AMP metabolism on fruiting body formation inSaccobolus platensis

Abstract The ascomyceteSaccobolus platensis Gamundi´& Ranalli requires light to produce apothecia. It has now been found that this light requirement can be satisfied by a 24-h pulse of white light at certain stages of the sexual cycle. The addition of exogenousN6,O2′-dibutyryl adenosine 3′,5′-cyclic monophosphate (db-cyclic AMP) to the dark growing mycelia could replace rather efficiently the inductory effect of light; cyclic AMP,N6-monobutyryl cyclic AMP, andO2′-monobutyryl cyclic AMP were less effective, while guanosine 3′,5′-cyclic monophosphate (cyclic GMP) was a very weak inducer. An inducing effect similar to that of db-cyclic AMP was obtained by the addition of 3-isobutyl-1-methylxanthine (MIX) or theophylline to cultures developing in darkness. In the presence of theophylline, endogenous cyclic AMP levels of dark-grown mycelia were several fold higher than those of control cultures. The cyclic AMP content of mycelia growing under different light regimes was measured and no significant differences were observed. However, cultures submitted to white light showed an increase in adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) and a decrease in cyclic AMP phosphodiesterase (3′,5′-cyclic AMP 5′-nucleotidohydrolase, EC 3.1.4.17) specific activities compared with the activities of dark-grown mycelia. The cyclic AMP phosphodiesterase activity was strongly inhibited by theophylline and by MIX. The possible role of cyclic AMP in the induction of apothecia in this species is discussed.

Extraction and characterization of polygalacturonase of Fomes sclerodermeus produced by solid-state fermentation

Polygalacturonase (PG) production by Fomes sclerodermeus using solid-state fermentation (SSF) was carried out. Maximal PG activity (26 U/gdw) was obtained between days 11 and 13 at the end of exponential growth. PG activity in the crude extract was more stable at pH 5-6 and 30 degrees C and had optimum activity at pH 5 and 50 degrees C. Optimal conditions for PG extraction were: one time extraction with Na2SO4 as solvent with 10 min. of agitation. In a scale-up system, PG activity per gram of dry substrate decreased about 60% compared with the activity obtained in an Erlenmeyer flask; however, high total PG activity was obtained.

Effect of light and nutrition on fruiting ofAscobolus biguttulatus

The influence of light and nutrition on fruit body development inAscobolus biguttulatus was studied. High C and N concentrations inhibited sexual reproduction. A wide variety of carbon sources supported the production of fertile apothecia. Among the nitrogen sources, urea and asparagine were the best, while inorganic salts resulted in very poor fruit body production. Light was an absolute requirement for apothecial production. When photoinduction was accomplished by single 24-h periods, the colonies were most receptive at the 5th day of growth. Among types of light, near ultraviolet light was the most effective.