Stabilization of a Heme-HNO Model Complex Using a Bulky Bis-Picket Fence Porphyrin and Reactivity Studies with NO.

Nitroxyl, HNO/NO, the one-electron reduced form of NO, is suggested to take part in distinct signaling pathways in mammals and is also a key intermediate in various heme-catalyzed NO interconversions in the nitrogen cycle. Cytochrome P450nor (Cyt P450nor) is a heme-containing enzyme that performs NO reduction to NO in fungal denitrification. The reactive intermediate in this enzyme, termed "Intermediate ", is proposed to be an Fe-NHO/Fe-NHOH type species, but it is difficult to study its electronic structure and exact protonation state due to its instability.

The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity.

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO.

Crystal structures of two heterotrimetallic dysprosium-manganese-sodium 12-metallacrown-4 complexes with the bridging ligands 3-hy-droxy-benzoate and 4-hy-droxy-benzoate.

The syntheses and crystal structures for the compounds tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ-3-hy-droxy-benzoato)dys-pro-s-ium(III)-tetra-manganese(III)sodium(I) ,-di-methyl-acetamide deca-solvate, [DyMnNa(CHO)(CHNO)(HO)]·10CHNO or [DyNa(4-OHben){12-MC-4}(HO)]·10DMA, , and tetra-μ-aqua--tetra-kis-{2-[aza-nid-yl-ene(oxido)meth-yl]phenolato}tetra-kis-(μ-3-hy-droxy-benzoato)dys-pros-ium(III)tetra-manganese(III)sodium(I) ,-di-methylformamide tetra-solvate, [DyMnNa(CHO)(CHNO)(HO)]·4CHNO or [DyNa(3-OHben){12-MC-4}(HO)]·4DMF, , and where MC is metallacrown, shi is salicyl-hydroximate, 3-OHben is 3-hy-droxy-benzoate, DMA is ,-di-methyl-acetamide, 4-OHben is 4-hy-droxy-benzoate, and DMF is ,-di-methyl-formamide, are reported. For both and , the macrocyclic metallacrown consists of an [Mn-N-O] ring repeat unit, and the domed metallacrown captures two ions in the central cavity: a Dy ion on the convex side of the metallacrown and an Na ion the concave side. The Mn ions are six-coordinate with an elongated tetra-gonally distorted octa-hedral geometry.

Making or Breaking Metal-Dependent Catalytic Activity: The Role of Stammers in Designed Three-Stranded Coiled Coils.

While many life-critical reactions would be infeasibly slow without metal cofactors, a detailed understanding of how protein structure can influence catalytic activity remains elusive. Using de novo designed three-stranded coiled coils (TRI and Grand peptides formed using a heptad repeat approach), we examine how the insertion of a three residue discontinuity, known as a stammer insert, directly adjacent to a (His) metal binding site alters catalytic activity. The stammer, which locally alters the twist of the helix, significantly increases copper-catalyzed nitrite reductase activity (CuNiR).