THE MARINE RED ALGA EUCHEUMA-SERRA J. AGARDH, A HIGH-YIELDING SOURCE OF 2 ISOLECTINS

Aqueous ethanolic extracts from five species of the genus Eucheuma (Rh odophyta) i.e. E. serra, E. amakusaensis, E. cottonii, E. gelatinae an d E. denticulatum, were examined for hemagglutinating activity with ve rtebrate erythrocytes. All the extracts tested agglutinated trypsin-tr eated sheep and rabbit erythrocytes as well as untreated sheep erythro cytes. From the extract of E. serra, which exhibited the highest activ ity, a lectin was purified by precipitation with cold ethanol followed by gel filtration to exhibit a single band on SDS-PAGE. The yield was surprisingly as high as 1000 mg from 100 g powdered alga. The purifie d lectin was further separated into two isoforms, designated ESA-1(90 mg) and ESA-2 (890 mg), by ion exchange chromatography. Both lectins s howed a single protein band with the same molecular weight of 29 000 o n SDS-PAGE and differed from each other only in isoelectric point (pI 4.75 for ESA-1 and pi 4.95 for ESA-2). Biochemical studies revealed th at both are monomeric proteins without a carbohydrate moiety. The hema gglutinating activities were stable over a wide pH range and at a rela tively high temperature. The activities were inhibited by a number of glycoproteins, but not by any of the monosaccharides and disaccharides tested. The lectins showed strong mitogenic activities for mouse lymp hocytes.