11S and 7S globulins of coconut (Cocos nucifera L.): purification and characterization

Total globulins extracted with 0.4 M NaCl in buffer from coconut endosperm separated into two peaks on gel filtration: peak I corresponding to 11S globulin or cocosin and peak II to 7S globulin with native molecular weights of 326 000 and 156 000, respectively. The percent composition of total globulins was estimated to be 11S, 86% and 7S, 14%. On SDS-PAGE, cocosin resolved into two closely migrating bands at approximately 34 000 (acidic polypeptide) and another set of 2 bands at 24 000 (basic polypeptide). Each set consisted of one darkly stained band and one lightly stained band. The 7S globulin consisted of three bands of 16 000, 22 000, and 24 000. Three isoforms of cocosin were identified after anion exchange chromatography. Cocosin, but not the 7S, was found to have disulfide bonds. Using periodic acid-Schiff's reagent, all of the bands of cocosin on SDS-PAGE were positive for carbohydrate. However, when con A-peroxidase was used, only the basic polypeptide stained positively for carbohydrate. For the 7S globulin, no carbohydrate group was detected using the PAS and con A-peroxidase tests. The 7S globulin was easily extracted with 0.10-0.15 M NaCl, whereas cocosin was extracted with 0.35 M NaCl. The N-terminal amino acid sequences of the 34 k band and 24 k band of cocosin were SVRSVNEFRXE and GLEETQ, respectively, and that of the 7S was EQEDPELQK.