A Crosslinked Cofactor in Lysyl Oxidase: Redox Function for Amino Acid Side Chains

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Abstract
A previously unknown redox cofactor has been identified in the active site of lysyl oxidase from the bovine aorta. Edman sequencing, mass spectrometry, ultraviolet-visible spectra, and resonance Raman studies showed that this cofactor is a quinone. Its structure is derived from the crosslinking of the ϵ-amino group of a peptidyl lysine with the modified side chain of a tyrosyl residue, and it has been designated lysine tyrosylquinone. This quinone appears to be the only example of a mammalian cofactor formed from the crosslinking of two amino acid side chains. This discovery expands the range of known quino-cofactor structures and has implications for the mechanism of their biogenesis.