Received for review December 27, 2004. Accepted March 4, 2005. This work was supported in part by grants to S.U. and N.M. from the Ministry of Education, Culture, Sports, Science and Technology of Japan and to S.U. from Fuji Foundation for Protein Research and The Salt Science Research Foundation.

Abstract:

Glycinin consists of five kinds of subunits, group I (A1aB1b, A1bB2, and A2B1a) and group II (A3B4 and A5A4B3). cDNAs for individual subunits were cloned by reverse transcription-polymerase chain reaction method and expressed in Escherichia coli using pET vector. The recombinant proglycinins were purified by ammonium sulfate fractionation and column chromatography in the form of homotrimers. Physicochemical properties such as molecular dimensions, solubility, surface hydrophobicity, thermal stability, and emulsifying ability of individual proglycinins were studied. Molecular dimensions were proportional to molecular size for all proglycinins except A2B1a. Solubility was intrinsic to each proglycinin. At the ionic strength of 0.5, all proglycinins except A1aB1b showed a very low solubility at acidic pH, but A1aB1b was soluble to higher than 60%. At ionic strength 0.08, all proglycinins exhibited isoelectric precipitation, although A2B1a and A1bB2 were not completely insoluble. The order of emulsifying ability (A1bB2 < A2B1a < A5A4B3 < A3B4 A1aB1b) was not of the same for surface hydrophobicity (A5A4B3 < A1aB1b A3B4 < A1bB2 < A2B1a) and thermal stability (A1bB2 A2B1a A5A4B3 < A3B4 A1aB1b).

Keywords: Glycinin; proglycinin; structure-physicochemical function relationship; solubility; thermal stability; soybean

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