Figure 5:

A model of nacre formation in P. f. martensii. In this model, new nacre (N) is formed in an organic matrix secreted by haemocytes or epithelial (Ep) cells beneath the mature nacre (M). Chitin provides the core of the polymer framework of the organic matrix. VWAP with chitin-binding domains binds to chitin and interacts with fibronectins and other VWAPs, forming the matrix networks. Asp-rich acid glycoproteins and acid GAGs function as the hydrogel substances. Tyrs catalyse the oxidation of tyrosine and dopamine and function in cross-linking and shell matrix maturation. Protease inhibitors, proteases, and other enzymes regulate the biosynthesis or degradation of the organic matrix.