Nickel Enzymes & Cofactors

Abstract

This review covers the structure and function of the eight known Ni enzymes, with a focus on the chemistry and biology of the metallocenter. For the Ni redox enzymes, the Ni ion exhibits versatility in redox properties in exploiting the +3/+2 (superoxide dismutase and hydrogenase), the +2/+1 (hydrogenase, CO dehydrogenase, acetyl‐CoA synthase, and methyl‐CoM reductase), and perhaps even reaching the 0 (acetyl‐CoA synthase) states for the redox enzymes. On the other hand, the nonredox Ni enzymes (urease, glyoxylase‐I, aci‐reductone dioxygenase) apparently remain in the +2 state during catalysis. The Ni site(s) in these enzymes adopt a wide variety of coordination environments; some form mononuclear square planar or octahedral complexes, while others are homo‐ or hetero‐ (with iron) dinuclear with oxo or thiolato bridges and still others join heteromultinuclear clusters. Acetyl‐CoA synthase contains the most complex Ni metallocenter yet described, which is a [4Fe–4S] 2+ cluster bridged by a cysteine thiolate to a binuclear NiNi center. The three‐dimensional structures of all these enzymes are known and some (acetyl‐CoA synthase, aci‐reductone dioxygenase, CO dehydrogenase, and superoxide dismutase) have been determined in the past two years leading to a significant reinterpretation of spectroscopic results. In many Ni enzymes, density functional theory has begun to play a major role in assigning active‐site structures and testing mechanistic hypotheses.

Investigation of the serum oxidative stress in broilers fed on diets supplemented with nickel chloride

“…In addition, Ni is a nutritionally essential trace metal for micro-organisms and plants [17]. Currently, eight Nicontaining enzymes have been identified [18].…”

Serpentinization as the source of energy, electrons, organics, catalysts, nutrients and pH gradients for the origin of LUCA and life

“…Such light isotope signatures (δ 13 C) in the range of –40‰ to –80‰ are generally interpreted to indicate the presence of methanogens (archaea) ( Arndt and Nisbet, 2012 ), but acetogens (bacteria) have a similarly light isotopic signature ( Blaser et al, 2013 ). Ultralight isotopes indicate the presence of the acetyl-CoA pathway of CO 2 fixation in primordial bacteria and archaea ( Tashiro et al, 2017 ), in line with its exergonic nature ( Berg, 2011 ), ancient physiology ( Rühlemann et al, 1985 ; Fuchs, 2011 ), abundance of metal cofactors ( Martin and Russell, 2003 ; Ragsdale, 2006 ) and carbon-metal bonds ( Martin, 2020 ), its dual role as a pathway of carbon and energy metabolism in acetogens and methanogens ( Martin and Russell, 2007 ) and in line with metabolic and phylogenetic reconstructions of LUCA ( Weiss et al, 2016 ).…”

(Benz-)imidazolin-2-ylidene-benzimidazolatonickel(II) Chelates: Syntheses, Structures, and Tuning of Noninnocent Chelate Ligand Behavior

“…This π delocalization provides a possibility for noninnocent behavior of the benzimidazolate moiety, which might otherwise not remain coordinated in different oxidation states without the aid of the strong NHC chelate. Redox-active or noninnocent ligands (NILs) are often found in nature, providing redox equivalents and/or stabilizing unpaired electrons in enzymatic reactions, and many metalloenzymes, including those containing Ni active sites, utilize imidazol­(at)­e from histidine residues in the ligand sphere around the metal atom(s). − Possible redox processes of cyclopentadienylnickel­(II) complexes containing a NIL (in the present work, this is 1′ – or 2′ – ) are summarized in Scheme .…”

“…Nickel is found most often in the oxidation states Ni II and Ni 0 ; , however, Ni I and Ni III may actually play a key role in several catalytic transformations − and in the activation of fundamentally important small molecules such as CO 2 , N 2 , H 2 , CO, and olefins. − ,− In these less common oxidation states nickel contains an unpaired electron. Ni I and Ni III complexes can be supported by several types of ligands, such as (pentamethyl)­cyclopentadienyl (Cp or Cp*), and by strong donor ligands. ,− The uses of noninnocent ligands and metal clusters are both methods, also found in nature, to provide stability to nickel radicals through the distribution of the unpaired electron over several atoms. − Complexes with a formal Ni III center are frequently supported by multidentate, often pincer-type or macrocyclic, ligands with N being the primary ligating atom. − …”