L-3,4-DIHYDROXYPHENYLALANINE (L-DOPA) IN ANODONTA-CYGNEA - VARIATION WITH ACIDOSIS

L-3,4-dihydroxyphenylalanine is present in the shell, mantle cells and fluids of the bivalve Anodonta cygnea. Normal conditions, representin g autumn and winter period, present high levels of L-DOPA in the fluid s and low levels in the mantle. However, data show that there is a dif ferent distribution of this compound all over the mantle area, and the portions with the most significant L-DOPA content are the siphon bord er and the mantle part adjacent to the curvature of the shell (next to the umbo). Acidic conditions, simulating internal acidosis that occur s in Anodonta cygnea during spring and summer, show a significant vari ation of L-DOPA, increasing in the mantle, mainly in the central part, and decreasing in the fluids. Moreover, results indicate that L-DOPA contributes to the formation of the pellicle formed under acidosis in the nacreous layer. These variations of L-DOPA with acidosis suggest t hat its synthesis is increased in the central mantle and all available L-DOPA is removed from the fluids to integrate the thin pellicle form ed in the nacreous layer of the shell. The recently formed periostracu m and the umbo have the highest L-DOPA content in the shell because th ey are sclerotized structures. These results suggest that the biominer alization and sclerotization processes of the shell are closely relate d to the integration of L-DOPA in the nacreous layer and in the perios tracum, respectively. The decrease of the internal pH appears as a rel evant switch to induce the production of this amino acid in the centra l mantle. (C) 1998 Elsevier Science Inc. All rights reserved.