The hydBGDA genes, which encode the four subunits /?, y, S and a of the [Ni-Fe] hydrogenase from the archaeon Pymcoccus furiosus, have been isolated and sequenced using a PCWIPCR-based strategy. From the sequence analysis it appears that the four structural genes are tightly linked and organized in a single transcription unit. The hydD and hydA gene products are related to the small and the large subunits of several archaeal and eubacterial [Ni-Fe] hydrogenases with an overall degree of sequence relatedness ranging from 35 YO to 50% (identity +similarity). In particular, the amino acid sequence motifs involved in the accommodation of nickel and iron-sulfur clusters are conserved. In addition, the database search revealed that the hydB and hydG gene products are homologous to the asrA-and asrB-encoded subunits of the sulf ite reductase enzyme from Salmonella typhimurium . This is particularly interesting in view of the recent finding that the P. furiosus hydrogenase appears t o be a bifunctional enzyme endowed with both proton-and sulfurreducing activities.

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Catalytic amounts of glucose oxidase from Aspergillus niger (GO) are active in the reduction of O2 to H2O2 in the presence of irradiated suspensions of TiO2 and isopropyl alcohol as electron donor. An explanation of this behaviour is given on the basis of the ability of the enzyme to capture electrons from the photoexcited TiO2 instead of its natural substrate, glucose. This process has a marked positive effect on both the oxidation of isopropyl alcohol to acetone and the formation of radical intermediates, which have been detected, for the first time, by EPR-spin trapping investigation.

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