No abstract

No abstract

An active site, cofactor-containing peptide has been obtained in high yield from bovine serum amine oxidase. Sequencing of this pentapeptide indicates: Leu-Asn-X-Asp-Tyr. Analysis of the peptide by mass spectrometry, ultraviolet-visible spectroscopy, and proton nuclear magnetic resonance leads to the identification of X as 6-hydroxydopa. This result indicates that, contrary to previous proposals, pyrroloquinoline quinone is not the active site cofactor in mammalian copper amine oxidases. Although 6-hydroxydopa has been implicated in neurotoxicity, the data presented suggest that this compound has a functional role at an enzyme active site.

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 epsilon-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.