CHARACTERIZATION OF ORGANIC MATRIX MACROMOLECULES FROM THE SHELLS OF THE ANTARCTIC SCALLOP, ADAMUSSIUM-COLBECKI

The highly acidic soluble organic matrix (SM) isolated from shells of the Antarctic scallop, Adamussium colbecki, was shown to consist of 1.5% carbohydrate by weight and 12.8% phosphate by weight. Total SM is composed of approximately 31% Asx, 29% Ser, and 18% Gly. Separation of the SM using RP-HPLC yielded a minimum of six protein fractions labeled RP-1 through RP-6 in order of elution off the column. The first fraction, RP-1, was found to be an effective inhibitor of calcium carbonate crystal nucleation in vitro suggesting a role for this protein in the regulation of shell mineralization. A less acidic fraction, RP-3, showed less inhibitory activity and dephosphorylation of RP-1 resulted in almost complete loss of inhibitory activity. Automated Edman degradation was used to sequence peptides generated by chemical cleavage of RP-1. Mild acid hydrolysis yielded peptides with sequences of N-S-G-D-D-D-D-G-G-OH, N-S-G-G-(S,G)-G-OH, and N-S-G-R-G-OH. Cleavage with hydroxylamine yielded peptides of N-D-D-D-D-D-D-D-D-OH, N-L-Y-Y-OH, and N-A-V-G-E-S-D-OH. These data suggest biochemical similarities between this SM and other SM proteins isolated from both calcium carbonate and calcium phosphate biominerals, and presents evidence of a primary domain structure similar to that described for oyster SM and phosphophoryn isolated from rat dentin.