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The origin of life is mostly divided into "genetics first" and "metabolism first" hypotheses. The former is based on spark-tube tests and organic species from meteorites and comets, and proposes a heterotrophic origin of life also consistent with the "RNA World" concept. The "metabolism first" hypothesis posits that life began autotrophically on minerals and/or hydrothermal vents. The lack of direct evidence means it is not possible to lend solid support to either hypothesis but the "metabolism first" option can be explored if a continuous geochemical, catalytically dynamic process is assumed. Using this approach, it is speculated that purine and pyrimidine synthesis originated on a mineral surface, which was later replaced by ATP. The same applies to redox processes where metal-bound hydrides could have been replaced by NAD., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrogenases (H 2 ases) are benchmark electrocatalysts for H 2 production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and wiring of H 2 ase through the introduction of a hierarchical inverse opal (IO) TiO 2 interlayer. This proton-reducing Si|IO-TiO 2 |H 2 ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias-free) water splitting by wiring Si|IO-TiO 2 |H 2 ase to a modified BiVO 4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO-TiO 2 |H 2 ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z-scheme that replaces the non-complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The combination of enzymes with semiconductors enables the photoelectrochemical characterization of electron-transfer processes at highly active and well-defined catalytic sites on a light-harvesting electrode surface. Herein, we report the integration of a hydrogenase on a TiO2 -coated p-Si photocathode for the photo-reduction of protons to H2 . The immobilized hydrogenase exhibits activity on Si attributable to a bifunctional TiO2 layer, which protects the Si electrode from oxidation and acts as a biocompatible support layer for the productive adsorption of the enzyme. The p-Si|TiO2 |hydrogenase photocathode displays visible-light driven production of H2 at an energy-storing, positive electrochemical potential and an essentially quantitative faradaic efficiency. We have thus established a widely applicable platform to wire redox enzymes in an active configuration on a p-type semiconductor photocathode through the engineering of the enzyme-materials interface., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Streptomyces actuosus tryptophan lyase (NosL) is a radical SAM enzyme which catalyzes the synthesis of 3-methyl-2-indolic acid, a precursor in the synthesis of the promising antibiotic nosiheptide. The reaction involves cleavage of the tryptophan Cα-Cβ bond and recombination of the amino-acid-derived -COOH fragment at the indole ring. Reported herein is the 1.8 Å resolution crystal structure of NosL complexed with its substrate. Unexpectedly, only one of the tryptophan amino hydrogen atoms is optimally placed for H abstraction by the SAM-derived 5'-deoxyadenosyl radical. This orientation, in turn, rules out the previously proposed delocalized indole radical as the species which undergoes Cα-Cβ bond cleavage. Instead, stereochemical considerations indicate that the reactive intermediate is a (·)NH tryptophanyl radical. A structure-based amino acid sequence comparison of NosL with the tyrosine lyases ThiH and HydG strongly suggests that an equivalent (·)NH radical operates in the latter enzymes., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)