Structural characterization of high molecular weight starch granule-bound proteins in wheat (Triticum aestivum L.).

摘要

Mature grains of wheat cv. Norin 61 (and barley cv. KI-29 and rice cv. Nipponbare for comparison) were ground, homogenized, filtered and the starch granule-bound proteins extracted and separated by SDS-PAGE after which peptide mapping and sequencingwere conducted. It was observed that the wheat starch granule-bound proteins included at least one protein with a molecular weight of 61 000 (Wx protein: starch granule-bound starch synthase) and 6 minor proteins with molecular weights of 115 000, 108 000, 100 000, 92 000, 80 000 and 15 000 (SGP-A1, -D1, -B1, -2, -3 and friabilin, respectively). Peptide mapping of SGP-A1, -D1, -B1, -2 and -3 indicated that the primary structures of SGP-A1, -D1 and -B1 were highly homologous but differed considerably from that of SGP-2. The internal sequences of peptides obtained from SGP-D1, -2 and -3 indicated that SGP-D1 and SGP-3 were structurally similar to rice soluble starch synthase, whereas SGP-2 had homology to rice starch branching enzyme 3. These results are in agreement with results of immunological and enzymatic studies and it is suggested that SGP-A1, -D1, -B1 and -3 are types of soluble starch synthases and that SGP-2 is a starch branching enzyme. Since the ratio of amylose to amylopectin influences the texture and quality of flour, the understanding of the regulation of starch synthesis and deposition by starch related enzymes is important for breeding.