To elucidate the properties of protein in seaweeds, protoplasts were used as a starting material. Protoplasts were isolated from 4 green seaweeds Ulva pertusa, U. fasciata, Enteromorpha linza, and Monostroma nitidum; from 2 browns Laminaria japonica and Undaria pinnatifida; and from 1 red Callymenia perforata. Proteins in protoplasts were then extracted with low (I=0.05) and high (I=0.5) ionic strength phosphate buffers (pH 7.5) and 0.1N sodium hydroxide, and analyzed for protein composition, SDS-polyacrylamide gel electrophoretic pattern, and amino acid composition.
Non-protein nitrogen was a major fraction (59.5% of the total nitrogen) in L. japonica. While water-soluble proteins were major fractions in green and red seaweeds, and these amounted to 30.5-69.5% of the total nitrogen. Salt-soluble protein was a predominant fraction (26.4% of the total nitrogen) only in U. pinnatifida. Electrophoretic patterns of the protein fractions consisted of many bands, and most of the patterns differed one another among species or protein fractions. Amino acid compositions were similar in all protein fractions except arginine in some protein fractions from U. fasciata, M. nitidwn, and C. perforata. Protein compositions and electrophoretic patterns differed much between protoplasts and thalli in all seaweeds.