CEMENT PROTEINS OF THE ACORN BARNACLE, MEGABALANUS-ROSA

Components of the proteinaceous cement secreted by barnacles have yet to be studied because of their insolubility. We solubilized and charac terized the proteins of secondary cement, which is produced when the b arnacle is detached from the substratum, in Megabalanus rosa. The ceme nt was fractionated, according to its solubility in aqueous formic aci d, into a soluble fraction, SF1 (21%); a fraction soluble after reduct ion, SF2 (37%); and a fraction insoluble after reduction, IF (42%). An alysis of the SF1 and SF2 by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that they contained three polypept ides (SF1-60 k, -57 k, -47 k) and one polypeptide (SF2-60 k), respecti vely. The amino acid compositions of these polypeptides were similar a nd their N-terminal amino acid sequences were identical. These polypep tides had an unusual amino acid composition, rich in Ser, Thr, Ala, an d Gly, like the tube cement of a marine polychaete, Phragmatopoma cali fornica. The IF, solubilized in aqueous formic acid after cleavage wit h cyanogen bromide, was shown by SDS-PAGE to contain eight fragment pe ptides (CB-peptides). N-terminal amino acid sequences of the CB-peptid es were also determined. We conclude that the barnacle cement is compo sed of at least two types of protein: highly hydroxylated protein in t he SF1 and SF2 and insoluble protein in the IF. The SDS-PAGE pattern o f CB-peptides from the secondary cement was identical to that of the p rimary cement produced while the barnacle is attached to a substratum. In addition, immunoblot analysis, using a polyclonal antibody against one of the CB-peptides from the secondary cement, also cross-reacted with a CNBr-fragment peptide of the primary cement. These results indi cate that the primary and secondary cements are similar in protein com position.