Electrophoretic Characterization and Immunological Localization of Coconut (Cocos nucifera L.) Endosperm Storage Proteins

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Abstract
Proteins extracted from coconut (Cocos nucifera L.) endosperm were analyzed using sodium dodecyl-sulfate-polyacrylamide gel electrophoresis, tube gel isoelectric focusing, and two-dimensional electrophoresis. Antisera to soybean 11S and 7S globulins were used with Western blotting techniques to test for immunological similarities. Endosperm was fixed and processed for light microscopy and for immunocytochemistry. The nonreduced proteins fractionated into four major bands, whereas the reduced proteins fractionated into seven major bands ranging from 55 to 17 kilodaltons (kD). All major bands were glycosylated and each consisted of at least two polypeptides with different isoelectric points. A minor band at 67 kD and two minor bands at 22 kD were recognized by antibodies to 7S soybean globulin and a major and minor band at 35 and 32 kD, respectively, were recognized by antibodies to 11S soybean globulins. An antibody raised against the 55 kD protein showed no cross reactivity with any other bands. Cellular structure differs depending on location within the endosperm, especially with respect to cell size and characteristics of the protein bodies. The cells are relatively thin-walled and contain abundant lipid bodies and protein bodies with included protein crystalloids. Distinct localization patterns are apparent for legumin, vicilin, and the 55 kD protein. Legumin (11S) and vicilin (7S) are present in the crystalloids, whereas the 55 kD protein is present only in the protein body matrix.

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