Impact of surface modification with gold nanoparticles on the bioelectrocatalytic parameters of immobilized bilirubin oxidase.

We unveil experimental evidence that put into question the widely held notion concerning the impact of nanoparticles on the bioelectrocatalytic parameters of enzymatic electrodes. Comparative studies of the bioelectrocatalytic properties of fungal bilirubin oxidase from Myrothecium verrucaria adsorbed on gold electrodes, modified with gold nanoparticles of different diameters, clearly indicate that neither the direct electron transfer rate (standard heterogeneous electron transfer rate constants were calculated to be 31±9 s(-1)) nor the biocatalytic activity of the adsorbed enzyme (bioelectrocatalytic constants were calculated to be 34±11 s(-1)) depends on the size of the nanoparticles, which had diameters close to or larger than those of the enzyme molecules.

[Metlegoglobin reductase from lupine nodules. Purification and properties]. / Metlegoglobinreduktaza kluben'kov liupina. Ochistka Svoistva.

The purification procedure and properties of metlegoglobin reductase from the soluble fraction of lupine (Lupinus luteus L.) nodules and from the proteins secreted by bacteroids Rhizobium lupini in vitro are described. The properties of both forms of enzyme were found to be similar. A metlegoglobin reductase preparation purified 125-fold with a yield of 21% was obtained. The enzyme is strictly specific to the cofactor (NADH). No substrate specificity was revealed. The enzyme reduces oxidized cytochrome c, Mb+, Lb+, Hb+ and exygen. The pH optimum for the enzyme is 7,4. The enzyme is inhibited by p-chloromercurybenzoate. In some properties the enzyme from lupine nodules is close to methemoglobin reductase from the erythrocytes. It was shown that apart from metlegoglobin reductase, bacteroids secrete some other proteins, which is indicative of a close interrelationship between the bacteroids and the plant in a symbiotic nitrogen-fixing system.

[Enzymatic reduction of legoglobin]. / Fermentativnoe vosstanovlenie legoglobina

During incubation in the buffer bacteroids Rizobium lupini liberate an enzymic system (ferri-Lb-reductase) capable of reducing ferri-Lb and ferri-Mb The hemoproteids reduction required the presence of cofactors (NADPH or NADH). The ferri-Lb-reductase activity was also found in the soluble fraction of nodules. It is assumed that bacteroids ferri-Lb-reductase, maintains Lb in a physiologically active reduced state into vegetable cells of the nodules "in vivo" as well.