A sulfated proteoglycan from the red alga Gracilaria verrucosa is a hemagglutinin.

1. A novel hemagglutinin was isolated from the red alga Gracilaria verrucosa and characterized as a sulfated proteoglycan with 92% carbohydrate content. 2. It is a dimer (MW 27,000 and MW 23,000); its molecular weight (MW) and isoelectric point are 49,000 and 3.8, respectively. 3. It agglutinates rabbit greater than horse greater than guinea pig greater than goose erythrocytes. 4. This activity is sensitive to heat, but insensitive to protease or periodate. It is not inhibited by simple sugars but by fetuin. 5. Since the periodate treatment of the rabbit erythrocyte lowers agglutination, this hemagglutinin is probably a lectin or a lectin-like molecule with complex saccharide specificity.