Salt-soluble seed globulins of various dicotyledonous and monocotyledonous plants - I. Isolation/purification and characterization

Detailed characterization of 21 purified seed globulins derived from both monocotyledonous and dicotyledonous plants indicated that globulins from both class types (as well as within the same class type) lay within a narrow molecular weight range between 300 000 and 370 000 Da and were composed of multiple subunits. In all cases, purified globulins could be classified as hetero-oligomers being composed of a non-equimolar ratio of various subunits. The vast majority of subunits forming these globulins were shown to be held together by non-covalent bond forces. A small percentage of linkages between subunits were also shown to be disulfide linked, in the case of dicotyledonous seed globulins. It was also found that the majority of subunits composing the dicotyledonous and monocotyledonous seed globulins examined fell within two very narrow molecular weight ranges, i.e. 20 000-27 000 and 30 000-39 000 Da and were believed to correspond to basic and acidic subunits, respectively. Unlike monocotyledonous seed globulins, globulins derived from dicotyledonous plants were found to undergo alkaline-induced dissociation due to electrostatic repulsion between subunits. The amino acid composition of both dicotyledonous and monocotyledonous seed globulins suggests that they have a storage role and may be similar proteins based on a high content of amides (glutamic acids-glutamine and aspartic acid-asparagine and arginine). From the results of the structural and chemical data obtained in this study, it is concluded that the 11S storage globulin, having several similar properties, exists in many leguminous and nonleguminous dicotyledonous plants as well as monocotyledonous plants. This similarity among 11S storage globulins could be due either to convergent evolution in response to a common functional need, or to common ancestry. (C) 1998 Elsevier Science Ltd. All rights reserved.