Calcification and its mechanism in the shore-crab, Carcinus maenas (L.)

Crustacean cuticle is strengthened by the deposition of lime. Calcification in general is usually attributed to the combined action of enzymes and to an organic seeding mechanism. The production of alkalinity by electrode action, resulting from diffusion of salt water through a protein membrane containing semiconducting substances, suggests that lime may be precipitated in this way. This theory is examined with particular reference to the shore-crab, Carcinus maenas (L.). Semiconducting materials in protein or cuticle were detected mainly by the conversion of the dye Nile blue sulphate to the alkaline form, the red base, on outward diffusion of salt. This is termed the ‘Nile blue brine’ reaction. When this treatment was applied to protein to which hydroquinone and calcium carbonate had been added, alkalinity was greatly enhanced by the further addition of the bicarbonate or ferrous ion. The reaction is then comparable to that in normal crab cuticle. Calcification of the cuticle in relation to semiconducting material has been studied through the moult cycle. Calcification at each stage occurs in regions which according to the electrochemical theory proposed are normally cathodic, supporting the view that such calcification is electrochemical in origin. The conduction mechanism is discussed with reference to the mechanism of charge transport and polarization. It is concluded that the essentials for calcification of the surface of an organism such as the crab are: processes which maintain the inside electronegative to the outside, the presence of semiconducting complexes in, the cuticle and the presence of sufficient lime in the environment.