Identification of Cultivar Differences in Seed Polypeptide Composition of Peanuts (Arachis hypogaea L.) by Two-Dimensional Polyacrylamide Gel Electrophoresis 1

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Seed polypeptides from several cultivars of peanut (Arachis hypogaea L.) have been compared by means of a two-dimensional polyacrylamide gel electrophoresis. Protein was extracted from the defatted peanut meal by homogenizing in 5 millimolar K2CO3-9.5 molar urea. After addition of Nonidet P-40 (2%, v/v) and dithiothreitol (0.5%, w/v) the solution was centrifuged at 25,000 g. This procedure led to solubilization of more than 95% of the total protein. The clear supernatant fraction was then subjected to two-dimensional polyacrylamide gel electrophoresis, employing isoelectric focusing in the first dimension and electrophoresis in presence of sodium dodecyl sulfate in the second. After examining several cultivars, it was possible to construct a composite map to include all of the polypeptide species found among all of the cultivars examined. At least 74 major and between 100 and 125 minor components were detectable by Coomassie blue staining. The majority of these had isoelectric points between pH 4.4 and 8.0, and molecular weights between 16,000 and 75,000. Several different cultivars have been compared using this method and it has been shown that considerable variation exists among the major polypeptides present. The method should prove valuable for analyzing different genotypes and selecting varieties with a particular storage protein make-up, as well as for following compositional changes that occur during seed development and germination.

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