title: The other Topa: formation of 3,4,5-trihydroxyphenylalanine in peptides.
abstract: Hydroxylation of peptidyl-3,4-dihydroxyphenyl-l-alanine (Dopa) was observed during tyrosinase incubation of a decapeptide related to the mussel adhesive protein mefp1. The reaction was carried out at high enzyme concentrations (700 units tyrosinase/micromol of tyrosine). The hydroxylation of tyrosines in the decapeptide proceeds sequentially. First, Tyr-9 is hydroxylated to Dopa, followed by hydroxylation of Tyr-5; finally, Dopa-9 is hydroxylated to Topa. Topa was identified as 3,4,5-trihydroxyphenylalanine (3,4,5-Topa) by comparison to known standards using amino acid analysis, derivatization with phenylisothiocyanate in combination with Edman sequencing, and matrix-assisted laser desorption mass spectrometry with time-of-flight. Two other peptides, not related to mussel proteins, were also found to form peptidyl-Topa upon incubation with tyrosinase. Although 3,4,5-Topa has been reported in the primary sequence of several peptides, its formation in vitro from tyrosine-containing peptides is novel. The formation of Topa would appear to be a function of tyrosinase rather than the nucleophilic addition of water to dopaquinone.
authors.affiliation: Surgical Sealants, Inc., Woburn, Massachusetts 01801, USA.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Burzio
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D004295:Dihydroxyphenylalanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism*; D006900:Hydroxylation; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D009842:Oligopeptides; D011506:Proteins; C037403:adhesive protein, mussel; C028702:5-hydroxydopa; D004295:Dihydroxyphenylalanine; D014442:Monophenol Monooxygenase