Atividade biológica, purificação e caracterização da lectina e toxina da alga marinha vermelha Gracilaria cornea J. Agardh

Abstract

The red marine alga Gracilaria cornea was analyzed in related to its chemical composition, showing predominance in the carbohydrate, magnesium and phosphorus. The crude extract of the alga agglutinated preferentially chicken erythrocytes treated with tripsin and it showed to be toxic to mice within 24 hours upon intraperitoneal injection (LD 50 104.0 mg/kg body weight). Thermal treatment of the crude extract to 50°C for 5 minutes completely inactived the haemagglutinating activity and to 60°C for 5 minutes the toxic activity. The purification procedure of the toxin and of the lectin was realized by application of the crude extract in hydrophobic interaction chromatography on column of PhenylSepharose CL-4B followed by gel filtration on Sephadex G-100 colunm. The carbohydrate content of 36.8% suggests that the toxin is a glycoprotein. It showed an molecular mass 71.56 kDa by gel filtration on Sephadex G-100 colunm and an molecular mass of 35 kDa by SDS-PAGE in the presence of b-mercaptoetanol. The lectin exhibited a single proteic band with apparent molecular mass of 56.4 kDa and under desnaturant conditions (SDS-PAGE in the presence de bmercaptoetanol) also exhibited a single proteic band with molecular mass of 66.0 kDa. Its carbohydrate content of 52.30% suggests that this protein is also a glycoprotein. The toxin is active for mice (LD 50 5.18mg/kg body weight) producing dyspnea, tonic-clônics convulsions and flaccid paralysis prior to death of the animal. The preliminary evaluations of the crude extract, lectin and toxin in the control on the tick B. micropius demonstrated that these proteics fractions affected the evolutionary cycle of the ectoparasite. The toxic effects of the crude extract and lectin were shown to be more intense than those of the toxin.