Gj. Mcdougall et al., TYROSINE RESIDUES ENHANCE CROSS-LINKING OF SYNTHETIC PROTEINS INTO LIGNIN-LIKE DEHYDROGENATION PRODUCTS, Phytochemistry, 41(1), 1996, pp. 43-47
Synthetic proteins composed of lysine (polylysine, PL) and a random co
-polymer of lysine and tyrosine (polylysine/tyrosine, PLT) were incorp
orated into lignin-like dehydrogenation polymers (DHPs) formed by the
peroxidase-catalysed polymerisation of coniferyl alcohol. The yield of
water-insoluble DHPs was greater in the presence of the tyrosine-cont
aining PLT than PL. Indeed, the increase in total yield with PLT was o
ften greater than could be accounted for if all the protein added had
become incorporated into the DHPs. A comparison of the Fourier transfo
rm infra-red spectra of the DHPs formed in the absence and presence of
synthetic proteins provided evidence that the presence of PLT had enh
anced the incorporation of coniferyl alcohol, albeit in a less cross-l
inked form, into DHPs. The insolubilisation of PL and PLT was suggeste
d by the presence of absorption bands in the infra-red spectra of thei
r respective DHPs that are characteristic of protein/amide moieties. T
he insolubilisation of PLT was confirmed by the release of material fr
om PLT-DHPs by digestion with trypsin. Therefore, this study provides
evidence that the presence of tyrosine residues may enhance the cross-
linking of proteins into lignin.