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Abstract. Fourteen antigenic constituents have been detected in A rachis hypogaea seeds. The major proteins of the classic arachin and conarachin fractions have been identified. Arachin contains 4 antigens (the major one called a-arachin) and conarachin contains 2 which have been called a,, and a2-conarachin. Structural differences between a-arachin, a1 and a2-conarachin are indioated by their different antigenic specificities. a-Arachin precipitates as a separate entity at low temperature. The action of trypsin on this protein induces an increase in electrophoretic mobility and prevents precipitation at low temperature. This enzyme has no detectable effect on a., and a,-conarachin.The proteins of the ootyledon and of the entire axis are quite similar in their immunoelectrophoretic patterns. However, quantitative and qualitative differences oocur between the proteins found in the cotyledon and those of the 1-millimeter tip of the axis. In the latter, there is a 4-fold smaller proportion of a-arachin than in the cotyledon. Immunoelectrophoretic analysis of subcellular preparations from cotytedons confirms that a-arachin is an aleurin and that c1-conarachin is a typical cytoplasmic protein. Large and small aleurone grains appear very similar in their qualitative antigenic composition.Proteins extracted from mature seeds of Arachis hypogaea appear heterogeneous by chromatography on DEAE-cellulose, ultracentrifugation and polvacrylamide gel electrophoresis (7, 10). Moreover, 2 of the reserve proteins, a-arachin and a-conarachin, associate or dissociate under different conditions of pH and ionic strength (17,18,19) to make the precise identification of individual components difficult or even uncertain. The fact that these 2 proteins exhibit similar electrophoretic mobilities (16) suggests structural similarities.Because of their high degree of specificity, immunological methods offer another approach for the study of peanut proteins. A general picture of the total proteins was established and the 2 major reserve proteins were characterized after submission to phys-

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