AbstractIon‐binding ligands and the conformations of some of the acidic matrix macromolecules present in the shells of a gastroped, a bivalve, and a cephalopod, are investigated in vitro by Fourier transform infrared spectroscopy. The complex assemblage of matrix constituents present in the EDTA‐soluble fraction is first separated into two quite different classes of macromolecules by a reversed‐phase chromatographic procedure. Infrared spectra indicate that the constituents of one class, which are proteins rich in aspartic acid, adopt the β‐sheet conformation upon binding calcium to the protein carboxylate groups. The second class of matrix constituents contains proteins rich in serine that appear to be associated with relatively large amounts of polysaccharide. They also bind calcium and upon doing so undergo a conformationa