Quinone Cofactors

Abstract

Quinone cofactors are used by several classes of enzymes, which catalyse the oxidation of biogenic amines and alcohols, to help catalyse these reactions. Before 1990 only one cofactor, the peptide‐derived pyrroloquinoline quinone had been identified. During 1990–2001, however, four new quinone prosthetic groups derived from naturally occurring amino acids were discovered. The first protein‐derived, nondissociable cofactor identified was 2,4,5‐trihydroxyphenylalanine quinone, designated topaquinone (TPQ) in copper amine oxidases . The discovery of TPQ led to the identification of a series of new quinone cofactors, including lysine tyrosylquinone (LTQ) in lysyl oxidase, cysteine tryptophylquinone (CTQ) in quinohaemoprotein amine dehydrogenase and tryptophan tryptophylquinone (TTQ) in bacterial methylamine dehydrogenase . These cofactors contribute electrophillic capabilities (and stabilise free radical intermediates) that naturally occurring, unmodified amino acid side chains are unable to provide. Key Concepts: Quinone cofactors are a class of cofactors used by many enzymes to catalyse the oxidation of amines and alcohols. Five quinone cofactors have been characterised: PQQ, TPQ, LTQ, TTQ and CTQ. PQQ is a peptide‐derived cofactor that involves the expression of six genes located within an operon. TPQ is derived from a precursor tyrosine and requires only Cu 2+ and O 2 for biogenesis. LTQ is formed by the cross‐linking of a tyrosine residue and a lysine residue, also requiring only Cu 2+ and O 2 . TTQ is formed by the cross‐linking of two tryprophan resides, with MauG completing biogenesis. CTQ, the most recently discovered quinone cofactor, is formed by the cross‐linking of a cysteine reside and a tryptophan residue.

Fabrication of Insoluble Elastin by Enzyme‐Free Cross‐Linking

“…As it is not synthesized in mammals its origin is rather explained as being a ubiquitous part of nutrition. [20] The presence of quinoenzymes is not limited to prokaryotes as several eukaryotic enzymes exist that depend on intrinsic quino-cofactors (for review see [21,22] ). Among them, lysyl tyrosylquionone (LTQ, Figure 1A) is the cofactor of LOX(L) enzymes and emerges from the cross-linking of an oxidized Tyr residue with the side chain of a Lys residue.…”

A Bioinspired Catalytic Aerobic Functionalization of Phenols: Regioselective Construction of Aromatic C–N and C–O Bonds

“…In this case, an ortho -imino phenol 5 is produced within the active site of lysyl oxidase (cf. TTQ) following condensation and redox-isomerization (Scheme B) . Although the immediate product of this coupling is ultimately hydrolyzed to the corresponding ortho -amino phenol 6 during enzymatic catalysis, we envisioned the initial steps leading to 5 as a uniquely efficient means of forming an aromatic C–N bond.…”