. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 170 J. H. WAITE AND S. O. ANDERSEN 10 0« 0-6 O I °« O r) 02. 225 25O 275 300 Wavelength nm FIGURE 5. UV-spectra of purified peaks E and G. Maximal absorbance occurs at 250 nm. Solvent was M acetic acid. quinone adducts (Mason and Peterson, 1965; Ito and Prota, 1977). A problem invariably arises, however, with respect to whether tyrosine or DOPA actually serves as the precursor for quinones. Many of the current assumptions about sclerotization have been influenced by the studies of Lissitzky. Rolland, Reynaud and Lasry (1
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 170 J. H. WAITE AND S. O. ANDERSEN 10 0« 0-6 O I °« O r) 02. 225 25O 275 300 Wavelength nm FIGURE 5. UV-spectra of purified peaks E and G. Maximal absorbance occurs at 250 nm. Solvent was M acetic acid. quinone adducts (Mason and Peterson, 1965; Ito and Prota, 1977). A problem invariably arises, however, with respect to whether tyrosine or DOPA actually serves as the precursor for quinones. Many of the current assumptions about sclerotization have been influenced by the studies of Lissitzky. Rolland, Reynaud and Lasry (1962) showing that DOPA transiently present in proteins in vitro is derived from tyrosyl residues by the direct action of mushroom polyphenoloxidase. Without compelling evidence, Pujol (1967) compared this reaction to the sclerotiza- tion of tyrosine-rich protein in Mytilus byssus. Similarly, many workers have since relied on the same reaction (often called autotanning) to explain sclerotiza- tion of tyrosine-rich proteins in molluscan periostracum. We consider the mushroom polyphenoloxidase reaction as inadequate for de- scribing sclerotization of periostracum. The following evidence now exists sup- porting a direct role of DOPA, not tyrosine, in the sclerotization of mytilid perio- stracum : it is known that periostracal phenoloxidase does nut catalyze the oxidation of tyrosine (Waite and Wilbur, 1976) ; that catecholic compounds (DOPA) are abundant in the periostracum-secreting cells of the mantle (Bubel, 1973) ; that DOPA is present at proportions of up to 4% in a soluble presclerotin (MW 20,000) of formic acid-extracted periostracum (Waite, Saleuddin and Andersen, 1979), and that DOPA, not tyrosine, decreases during the major period of sclerotization between the margin and first annulus. Of course, DOPA still owes its existence to a post-translational modification of some tyrosyl residues by o-hydroxylation (Waite, Saleuddin and Andersen, 1979), but this event probably o
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