STRUCTURAL CHARACTERIZATION OF HIGH-MOLECULAR-WEIGHT STARCH GRANULE-BOUND PROTEINS IN WHEAT (TRITICUM-AESTIVUM L)

Starch granule-bound proteins in endosperms of common wheat (Triticum aestivum L.) included at least one major protein with a molecular weig ht of 61,000 (Wx protein: starch granule-bound starch synthase) and si x 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, r espectively). Peptide mapping of SGP-A1, -D1, -B1, -2, and -3 indicate d that the primary structures of SGP-A1, -D1, and -B1 are highly homol ogous but differ considerably from that of SGP-2. The internal sequenc es of peptides obtained from SGP-D1, -2, and -3 showed that SGP-D1 and SGP-3 are structurally similar to rice soluble starch synthase, where as SGP-2 has homology to rice starch branching enzyme 3. These results are in agreement with results of immunological and enzymatic studies suggesting that SGP-A1, -D1, -B1, and -3 are types of soluble starch s ynthases and that SGP-2 is a starch branching enzyme.