Models for the Active Center of Pterin‐Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands

Abstract

The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoV'02(LN-S,)] (8; LN-S, = pyridine-2,6-bis(methanethiolato)) with 5,6,7&tetrahydropterin (7)'2 HCl (H,Ptr '2 HC1). The complex crystallizes, with a non-coordinating CI-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4)A,P = 120.36(3)0, a n d Z = 8. Weinterpret 9as [Mo"O(LN-S2)(Hf-q-H,Ptr)]Cl (q = quinonoid; H,Ptr = dihydropterin), i e . , a Mo" monooxo center coordinated by a pyridine-2,6-bis(methanethiolat0) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H20-soluble complex 9 reacts with the natural enzyme subsuate DMSO very slowly, possibly due to the lack ofeasily dissociable ligands at the metal center.Introduction. -The chemistry and structure of metalloenzymes containing hydrogenated pterins') are currently intensive fields of research. The 6/?-5,6,7,8-tetrahydro-~-biopterin') (1; H4Bip3)) plays an important role as a cofactor in the iron-or copper-dependent phenylalanine hydroxylases and other amino-acid hydroxylases [2] and in the ironcontaining NO synthase [3]. A large group of molybdoenzymes utilizes molybdopterin, a hydrogenated pterin component, in the molybdenum cofactor 2 (Mo-co 2). These molybdenum enzymes catalyze 0-transfer reactions such as those of dimethyl-sulfoxide reductase, sulfite oxidase, and xanthine oxidase [4]. Mo-co is also present in the formylmethanofuran dehydrogenase of methanogenic bacteria [5], and recently molybdopterin has been identified as a component of the active center of several tungsten-containing enzymes [6]. The proposed structures of Mo-co 2 had two main features: a hydrogenated pterin and coordination to the molybdenum ion by an enedithiol group attached as a side chain to the pterin. The oxidation state of the pterin in Mo-co has been a point of

Molybdenum−Pterin Chemistry. 2. Reinvestigation of Molybdenum(IV) Coordination by Flavin Gives Evidence for Partial Pteridine Reduction

“…Our interest in eq 1 relates to an ongoing project to systematize the compatibility of oxidation states in molybdenum complexes of pteridines. For example, it is observed that Mo(VI), but not Mo(IV), readily reacts with fully reduced tetrahydropterins , whereas Mo(0) and Mo(IV) yield complexes of oxidized pterins. In contrast, Mo(VI) reacts only sluggishly, if at all, with oxidized pterins .…”

Regulation of Redox Potential of a Pterin Derivative Bound to a Ruthenium(II) Complex by Intermolecular Hydrogen Bonding with Nucleobases

“…[8][9][10][11] Among the complexes, Ru II complexes have been revealed to be useful for evaluating the redox potentials of the pterin ligand and for elucidating the PCET processes. [8][9][10][11] Among the complexes, Ru II complexes have been revealed to be useful for evaluating the redox potentials of the pterin ligand and for elucidating the PCET processes.…”

“…Transition-metal complexes of pterin and their derivatives have been synthesized and characterized to demonstrate mainly their structures and redox behaviors. [8][9][10][11] Among the complexes, Ru II complexes have been revealed to be useful for evaluating the redox potentials of the pterin ligand and for elucidating the PCET processes. [12,13] We have employed a Ru II -TPA unit (TPA = tris(2-pyridylmethyl)amine) as a platform to obtain Ru II -pterin complexes, which exhibited reversible redox waves for the pterin ligands to afford fairly stable radical species that were spectroscopically well-characterized.…”

Effect of Molybdenum on The Activity of Molybdoenzymes

“…A -the proposed structure of the pterine cofactor [9]. ; B-the structure of the cofactor first discovered in the aldehyde oxidoreductase of P. Furiosus [10]; C -the structure of the pterine cofactor -guanosine -dinucleotide present in the reductase of R. sphaeroides DMSO [11]. Integration of Mo in MoCo in two variants allows placing Mo in the active center of the protein, thereby controlling its redox properties and aligning the pterin ring system for electron transfer into Mo or out of it [12].…”