Peroxidase catalyzed conjugation of peptides, proteins and polysaccharides via endogenous and exogenous phenols.

The research was directed towards peroxidase mediated cross-linking of proteins and polysaccharides. Two approaches were explored, cross-linking by use of ferulic acid (FA)oand cross-linking by use of catechol. Within each approach, first model studies were performed with small peptides, of which the findings were applied in subsequent studies with proteins. First, a kinetically controlled incubation that leads to covalently coupled adducts of the tripeptide Gly-Tyr-Gly (GYG) and FA, catalyzed by horseradish peroxidase (HRP) is described. Next, two series of covalent adducts of GYG and FA, comprising dehydrogenatively polymerized FA on the GYG tyrosine were identified. Cross-linking of holo- and apo‑a‑lactalbumin was subsequently explored. Oligomerization ofa‑lactalbumin was observed and a direct relation between protein conformation and extent of oligomerization was shown. Application of the findings with GYG, combined with those ofa-lactalbumin homo-cross-linking ledto the modification ofa-lactalbumin with FA. The degree of polymerization ofa-lactalbumin was reciprocal to the incident concentration of free FA. Next, cross-linking of FA-containing arabinoxylans withb-casein is described. Maximal formation of protein-arabinoxylan conjugates were formed at high protein to arabinoxylan ratios in combination with a low H ₂ O ₂ concentration and a long reaction time. Finally, the use of catechol in peroxidase catalyzed modification of aminoacids andproteins was studied . Covalent attachment of catechol to the side chain of the amino acids tyrosine and histidine was unambiguously proven by tandem MS ofthe adducts. Cross-linking of globular proteins yielded oligomeric adducts whereas cross-linking ofb-casein yielded high molecular weight polymers. Two mechanisms for the cross-linking of catechol with proteins were proposed.