The globulins of the ground nut. (Arachis hypogaea) I. Investigation of arachin as a dissociation system.
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alpha-Conarachin and alpha-arachin are metabolized differently during germination. The amount of alpha-conarachin decreases without the appearance of antigenic intermediary compounds. alpha-Arachin retains its original antigenic structure and becomes more anodic during germination, but a number of intermediary proteins, differing widely in electrophoretic mobility, form up to 14 days germination. The electrophoretic shift of alpha-arachin, detectable after 1 day of germination, might be caused by progressive deamidation of glutamine and asparagine. Decreases in amide content of protein extracted after germination support the hypothesis and suggest that alpha-arachin provides the first source of ammonia to the new seedling.New antigenic proteins are synthesized in both roots and cotyledons during germination. Some appear organ specific, whereas others are identical in both the cotyledons and the roots. Appearance and disappearance of each new protein is unique with respect to period of germination and hence might correspond to specific events of germination.
Crude peanut protein fractions from raw and roasted peanuts were examined in the RAST with 10 sera from patients showing clinical peanut sensitivity. The radioactive uptake results, which were generally high, did not reveal any distinguishable pattern. Two commercially available peanut proteins, peanut lectin and phospholipase D, gave poor RAST responses. Three purified peanut proteins, alpha-arachin, conarachin I, and concanavalin A-reactive glycoprotein, all gave significant RAST results that were generally lower than those obtained with the crude extracts. The extent of RAST inhibition obtained with these materials was inversely related to their abundance in the total peanut protein. Crossed immunoelectrophoresis with extracts from raw and roasted peanut indicated the presence of 22 and 10 anodically migrating antigens, respectively. Sixteen IgE binding antigens were revealed for raw peanut and seven for roasted peanut after incubation with a mixed serum from the 10 patients in crossed radioimmunoelectrophoresis (CRIE) using 125I-labeled anti-IgE. CRIE plates treated with individual serum samples showed that all the patients had specific IgE for the major antigen peak, which has been tentatively identified as alpha-arachin. This major storage protein of peanut, which is known to be particularly heat resistant; may be of greater clinical significance than its apparently low RAST activity would seem to indicate.
Subcellular fractions from the cotyledon obtained by differential and density gradient centrifugation, and extracts of total proteins from both cotyledon and axial tissues were analyzed by diethylaminoethyl cellulose chromatography, zone electrophoresis, ultracentrifugation, immunodiffusion, and immunoelectrophoresis. Fractionation and characterization of proteins in subcellular organelles of the peanut reaffirm that alpha-arachin is located in the protein bodies of the cells. Results obtained by diethylaminoethyl cellulose chromatography of subcellular fractions suggest that some of the conarachin proteins are cytoplasmic. alpha(1)-Conarachin is cytoplasmic, and alpha(2)-conarachin is particle-bound. alpha-Arachin and alpha(2)-conarachin predominate in the cotyledon. Quantitative differences for other proteins were also observed. Although qualitative similarities are apparent by immunoelectrophoresis, major differences were observed in the sedimentation patterns, zone electrophoreograms, and in the diethylaminoethyl cellulose chromatograms of total protein extracts from the cotyledon and the axis.
Peanuts are one of the most allergenic foods. The allergic reactions may vary in severity from mild urticaria to severe anaphylactic episodes and death. The prevalence of peanut sensitivity is unknown, but it may affect as many as 10% of allergic individuals. The chemistry of peanut proteins has been extensively studied. Two major protein fractions have been prepared from saline extracts of peanut flour, arachin and conarachin. A major peanut allergen termed "Peanut-1" has been isolated. However, a number of protein constituents, including the arachin and conarachin fractions, have been shown to be allergenic. The ability to diagnose peanut sensitivity accurately has been hampered by the lack of standardized peanut extracts. However, efforts are under way to prepare such standardized reagents. Treatment consists of avoiding peanut protein products and using self-administered epinephrine. A number of peanut protein-containing products are allergenic, although peanut oil is not. The peanut-allergic consumer should be instructed to carefully read labels of foods. This can at times, however, be misleading, because certain foods may be inadvertently contaminated by peanut proteins.
A concanavalin A-reactive glycoprotein allergen has been isolated from peanut (Arachis hypogaea). The allergen was separated by affinity chromatography and purified by gel permeation and ion-exchange chromatography. The monomeric molecular weight is 65,000 and the pI is 4.6. The presence of one cysteine residue per molecule results in some dimer formation. Concanavalin A-reactive glycoprotein is a potent allergen for peanut-sensitive patients in both in vivo and in vitro tests. It is allergenically stable, on in vitro examination, at temperatures of up to 100 degrees C and over the pH range 2.8-10. Removal of the carbohydrate moiety failed to eliminate the allergenicity. Concanavalin A-reactive glycoprotein is identified in the crossed immunoelectrophoretic pattern as a major antigen of peanut protein extract but its structural characteristics indicate that it is probably not a component of the major storage-protein complex, arachin.
The cupin family comprises a family of proteins possessing a common beta-barrel structure that is thought to have originated in a prokaryotic ancestor. This structural motif is found as a single domain in fungal spherulins, fern sporulins and the germins/oxalate oxidase proteins of plants, while the globular storage proteins of plants, called legumins (11 S) and euvicilins (7 S), are two-domain cupins. The 11 S globulins are hexameric heteroligomeric proteins of M (r) approximately 360000, with each subunit comprising an acidic 30000-40000- M (r) polypeptide that is disulphide-linked to a 20000- M (r) basic polypeptide. A number of cupins have been identified as major plant food allergens, including the 7 S globulins of soybean (beta-conglycinin), peanut (conarachin; Ara h 1), walnut (Jug r 2) and lentil, and the 11 S globulins of peanut (arachin; Ara h 3), soybean (glycinin) and possibly also coconut and walnut. Other members of the cupin superfamily have not been identified as allergens, with the exception of one germin (germination-specific protein) from pepper. Cupins are generally very stable proteins. A summary of our current knowledge of allergenic seed storage globulins will be presented, together with an overview of cupin structure and stability properties, as illustrated by the allergenic soya globulins, glycinin and beta-conglycinin.
By varying the ratio of succinic anhydride to the protein, glycinin, one of the major fractions of soybean proteins, is succinylated to various levels. Sedimentation velocity experiments indicate the dissociation of the protein due to succinylation. Viscosity increases and a blue shift occurs in the absorption spectrum. The rate of proteolysis increases. Both dissociation and denaturation of the protein appear to occur. The effect of syccinylation on glycinin and arachin, the major protein of groundnuts, appears to be different.