PHYSICOCHEMICAL PROPERTIES OF PURIFIED ISOFORMS OF THE 12S SEED GLOBULIN FROM MUSTARD SEED (BRASSICA-ALBA)

The 12S mustard seed globulin from Brassica alba was isolated from a v ariety of extraction solutions (i.e., 1.0(M) NaCl, pH 7.5 (mu = 1.0); 32.6/2.6 mM KH2PO4/K2HPO4, pH 7.5, containing 0.4(M) NaCl (mu = 0.5) a nd distilled water, pH 7.5, mu = 0. Gel filtration chromatography of t he crude globulin from the various extracts revealed two heterogeneous forms of the globulin; i.e., a polymerized (490kDa) and non-polymeriz ed (304kDa) form. Further purification of the non-polymerized form by anion-exchange chromatography indicated the presence of two isoforms. Characterization of one of these isoforms (i.e., isoform B) from the v arious extractions indicated the following: pi of 7.10, thermal denatu ration temperature in the range (89.73-90.16 degrees C), identical ami no acid composition that was particularly high in glutamic/glutamine r esidues, and a similar subunit composition. Isoform B globulins from a n extraction with a high ionic strength solution had overall comparabl e lower negatively and higher positively charged surfaces above and be low their pls, respectively; similar secondary and tertiary structures ; and similar solubility and spectroturbidity profiles compared to tho se globulins extracted with distilled water. The isoform B globulins f rom all three extractions were found to be cryoprecipitable at low tem peratures.