Isolation and Characterization of a D-Galactose-binding Lectin from the Acorn Barnacle Balanus rostratus

The hemolymph of the acorn barnacle Balanus rostratus showed hemagglutinating activity and inhibition of calcium carbonate crystallization. A lectin having D-galactose-binding specificity was isolated from the hemolymph by a combination of affinity chromatography on acid-treated agarose gel and HPLC. The purified lectin was dependent on the presence of calcium ion for hemagglutinating activity. In SDS-PAGE, it gave one protein band (25 kDa) under a reduced condition, while it gave two components (35 and 95 kDa) without a reducing agent. The molecular mass of the intact lectin was estimated to be 120 kDa by HPLC on TSK G-3000SW. Isolectric point was determined to be pH 4.4. The same amino-terminal sequence, Tyr-Val-Ser-Asn-Gln-Ser-Val-Glu-Pro-Asp-Ser-Ala-Asp-Thr-Ala, was obtained with the purified lectin as well as the components observed in SDS-PAGE. The purified lectin did not inhibit calcium carbonate crystallization at 1 mg/30 ml, although the hemolymph inhibited the crystallization at 0.1 mg protein/30 ml. The inhibitory factor(s) was an acidic and small molecular-weight compound(s).