Abstract
Crushed exoskeletons of the coral, Astrangia astrangia, were treated with sodium
hypochlorite (1.5%), SDS (0.5%) and then decalcified with EDTA. Upon purification by
affinity chromatography extracellular proteins with Mr of 31, 53, and 63 kDa were
distinguished using SDS/PAGE gel. The proteins appear to be extracellular isozymes of
carbonic anhydrase (CA). Bovine serum CAII antibodies cross-reacted with the proteins
isolated via affinity chromatography (ELISA and Western Blots). High CA enzyme
activity and the inhibition of CA with acetazolamide, all support the contention that an
extracellular CA is present in the exoskeleton. Cleaning the crushed exoskeleton with
both SDS and sodium hypochlorite to remove cellular proteins that are not entombed in
the calcite prior to CA extraction we assert that CA is secreted extracellularly along with
the matrix proteins. The total water-soluble proteins (WSP) in the exoskeleton of the
coral, A. astrangia, was 14 + 7 mg - protein/lOOg exoskeleton whereas CA isozymes
represent 224 ± 108 |Xg - protein/lOOg exoskeleton (N=6) or 1.71% the total WSP. These
data illustrate that coral extracellular CA isozymes do function in exoskeleton
mineralization by maintaining the bicarbonate concentrations at equilibrium so as to
maintain the availability of carbonate ions used in mineralization.
