. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 6. Sclerotization in locust cuticle (A) and Mytilus periostracum (B). Asterisks in A signify side chain carbons activated during /3-sclerotization. Structures la-c are catechols : II a-b are quinones. ing the products of aromatic cross-links in molluscan periostracum rather than the precursors. Unfortunately, nothing is known about the fate of DOPA following its oxidation to quinones in periostracum. One would assume that DOPA-quinones react with certain amino acid residues to form intermolecular cross-links. Lysine m
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FIGURE 6. Sclerotization in locust cuticle (A) and Mytilus periostracum (B). Asterisks in A signify side chain carbons activated during /3-sclerotization. Structures la-c are catechols : II a-b are quinones. ing the products of aromatic cross-links in molluscan periostracum rather than the precursors. Unfortunately, nothing is known about the fate of DOPA following its oxidation to quinones in periostracum. One would assume that DOPA-quinones react with certain amino acid residues to form intermolecular cross-links. Lysine may be such a reactive residue, but our results are not yet conclusive about this. The observation by Morrison, Steele and Banner (1969) that quinones in vitro are capable of reacting with almost all amino acids could portend great difficulty in the isolation of specific cross-links from periostracum. Sclerotization of exoskeletal proteins has been exploited throughout the animal kingdom, producing structures with a diversity of physical properties appropriate to the needs of the organism. A comparison of Sclerotization of locust cuticle with that of Mytilus periostracum reveals striking similarities as well as differences. In both, the oxidation of catecholic precursors mediates protein Sclerotization. However, in the locust cuticle (Fig. 6-A), the catechol, N-acetyldopamine, is of low molecular weight and freely diffusable. During Sclerotization, it can be con- verted to either a quinone or a catechol with activated side chain (/?-sclerotization). Thus, in the locust, Sclerotization can be modulated by the local concentration of N-acetyldopamine relative to protein, and by the ratio of quinone-tanning to /?-sclerotization (Andersen, 1974). In Mytilus periostracum (Fig. 6-B), protein with tightly bound DOPA residues is secreted from the mantle and cross-linked as the oxidized DOPA quinones react with available nucleophilic groups. Although less sophisticated than Sclerotization
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