Methylation of Lys residues on histone proteins is a well known and extensively characterized epigenetic mark. The recent discovery of lysine-specific demethylase 1 (LSD1) demonstrated that lysine methylation can be dynamically controlled. Among the histone demethylases so far identified, LSD1 has the unique feature of functioning through a flavin-dependent amine oxidation reaction. Data base analysis reveals that mammalian genomes contain a gene (AOF1, for amine-oxidase flavin-containing domain 1) that is homologous to the LSD1-coding gene. Here, we demonstrate that the protein encoded by AOF1 represents a second mammalian flavin-dependent histone demethylase, named LSD2. The new demethylase is strictly specific for mono-and dimethylated Lys 4 of histone H3, recognizes a long stretch of the H3 N-terminal tail, senses the presence of additional epigenetic marks on the histone substrate, and is covalently inhibited by tranylcypromine. As opposed to LSD1, LSD2 does not form a biochemically stable complex with the C-terminal domain of the corepressor protein CoREST. Furthermore, LSD2 contains a CW-type zinc finger motif with potential zinc-binding sites that are not present in LSD1. We conclude that mammalian LSD2 represents a new flavindependent H3-Lys 4 demethylase that features substrate specificity properties highly similar to those of LSD1 but is very likely to be part of chromatin-remodeling complexes that are distinct from those involving LSD1.Histones pack the eukaryotic DNA into the nucleosome, the basic unit of chromatin (1). These highly conserved proteins are not merely spools to wind DNA, but they rather regulate gene expression by modulating the activity of the transcriptional machinery. This is achieved through recognition of histone post-translational modifications by specific transcription factors, according to a scheme dictated by the so-called "histone code" (2, 3). Methylation of Lys residues on the histone N-terminal tails is one of the most extensively characterized epigenetic marks, being involved in the regulation of a plethora of fundamental processes such as heterochromatin formation, X-chromosome inactivation, and DNA repair (4, 5). The recent discovery of lysine-specific demethylase 1 (LSD1) 3 demonstrated that lysine methylation can be dynamically controlled and is not a static epigenetic mark as thought in the past (6, 7). LSD1 specifically acts on mono-and dimethylated Lys 4 of histone H3 through an oxidative process that requires FAD as essential redox cofactor (Fig. 1a). More recently, several other histone demethylases have been uncovered; they feature the property of containing a JmjC catalytic domain that carries out the reaction through an iron-dependent mechanism (8). The JmjC enzymes are able to act on trimethylated lysines, which is mechanistically impossible for flavin-catalyzed oxidative demethylation reactions (7). Histone demethylases have been found in association with a number of chromatin-remodeling complexes and are involved in many diverse transcriptional programs (9...

Water‐stable metal halide perovskites could foster tremendous progresses in several research fields where their superior optical properties can make differences. In this work we report clear evidence of water stability in a lead‐free metal halide perovskite, namely DMASnBr3, obtained by means of diffraction, optical and X‐ray photoelectron spectroscopy. Such unprecedented water‐stability has been applied to promote photocatalysis in aqueous medium, in particular by devising a novel composite material by coupling DMASnBr3 to g‐C3N4, taking advantage from the combination of their optimal photophysical properties. The prepared composites provide an impressive hydrogen evolution rate >1700 μmol g−1 h−1 generated by the synergistic activity of the two composite costituents. DFT calculations provide insight into this enhancement deriving it from the favorable alignment of interfacial energy levels of DMASnBr3 and g‐C3N4. The demonstration of an efficient photocatalytic activity for a composite based on lead‐free metal halide perovskite in water paves the way to a new class of light‐driven catalysts working in aqueous environments.

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The lactoperoxidase (LPO)-catalyzed oxidation of p-phenols by hydrogen peroxide has been studied. The behavior of the enzyme differs from that of other peroxidases in this reaction. In particular LPO shows several catalytic intermediates during the catalytic cycle because of its capability to delocalize an oxidizing equivalent on a protein amino acid residue. In the phenol oxidation the enzyme Compound I species, containing an iron-oxo and a protein radical, uses the iron-oxo group at acidic pH and the protein radical in neutral or basic medium. Kinetic and spectroscopic studies indicate that the ionization state of an amino acid residue with pKa 5.8 +/- 0.2, probably the distal histidine, controls the enzyme intermediate forms at different pH. LPO undergoes inactivation during the oxidation of phenols. The inactivation is reversible and depends on the easy formation of Compound III even at low oxidant concentration. The inactivation is due to the substrate redox potential since the best substrate is that with lowest redox potential, while the worst substrate has the highest potential. This strongly indicates that Compound II, formed during catalytic turnover, has a low redox potential, making easier its oxidation by hydrogen peroxide to Compound III. The dependence of LPO activity on the phenols redox potential suggests that the protein radical where an oxidizing equivalent can be localized is a tyrosyl residue.