ABSORPTION AND FLUORESCENCE STUDY OF TYROSINE‐DERIVED CROSSLINKING AMINO ACIDS FROM COLLAGEN

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Abstract
Isotrityrosine, an isomer of trityrosine with an ether linkage, is a new crosslinking amino acid recently found in cuticle collagen of Ascaris lumbricoides. The absorption and fluorescence spectra of this new amino acid were examined and compared with other tyrosine‐derived crosslinking amino acids. Isotrityrosine showed UV absorption maximum at 283 nm in acidic and neutral solutions and at 303 nm in strongly basic solution. The wavelengths are almost the same with those at dityrosine and trityrosine. The values of pKa, for chromophore phenols are 7.5 and 11.0. This means that two proton dissociations occur progressively one by one. Boric acid did not have any influence on isotrityrosine, though the effect on dityrosine and trityrosine was substantial. These facts mentioned above may suggest structural inequality of two phenols in an ether‐linked isomer. The wavelength of emission maximum was 450 nm, which was the longest wavelength among relative compounds examined. The fluorescence quantum yield was as small as 0.027, and the value was about one‐tenth of those of dityrosine and trityrosine. Isotrityrosine was also found in cuticle collagen of other worms which belong to the phylum nematoda.