Determination and quantification of the kokumi peptide, γ-glutamyl-valyl-glycine, in commercial soy sauces.
β-Conglycinin, and abundant storage protein in soybean (Glycine max (L.) Merr.) seeds, is a trimeric protein consisting of various isomers containing the three subunits, α′, α and β. Accumulation of the β-subunit is unique because it appears to be regulated by a variety of developmental and environmental signals. In this paper we describe the isolation and characterization of a genomic clone encoding the β-subunit of β-conglycinin. The genomic clone was characterized by restriction-enzyme mapping and partial DNA sequence analysis, by immunoprecipitation of a hybrid-selected invitro translation product, and by RNA blot hybridization reactions. An mRNA of approx. 1700 nucleotides hybridized to an internal 2-kilobase (kb) region of this 4.4-kb cloned DNA restriction fragment and was translated to yield a polypeptide with an approximate molecular weight of 48 kilodalton. This polypeptide is immunoprecipitable by antibody against β-conglycinin and is of appropriate size to represent the precursor polypeptide of the β-subunit. When this sequence was used as a probe in RNA blot hybridization experiments, the β-gene transcript was first detected by stage K and accumulated through stage O during soybean seed development, coincident with appearance of the β-subunit. Partial DNA sequence analysis of the 5′ end of the gene confirmed that the isolated gene encoded a β-subunit, based upon the previously reported amino terminal sequence for this protein. Genomic DNA blot hybridization analyses indicate that multiple DNA restriction fragments are highly homologous to this cloned β-gene sequence.