Abstract
The amylopectin which is the main constituent of starch granule is produced by the action of soluble starch synthases(SSS), starch branching enzymes(SBE), and starch debranching enzymes(DBE). Especially, DBEs; isoamylase(ISA) and pullulanase(PUL) play a crucial role in formation of multiple cluster structure of amylopectin molecule.
In this study, we have purified and characterized ISA from developing barley endosperm. SDS-PAGE analysis and immunochemical analysis revealed that ISA is hetero-oligomeric protein composed of two distinct polypeptides, 80kDa and 85kDa. Two ISA subunit genes were isolated by screening of a cDNA library from immature seeds harvested at two weeks after head emergence. The sequence homology of ISA cDNAs between 80kDa and 85kDa was 47 percent. Therefore, it is suggested that the two ISA subunits encoded by 80kDa and 85kDa cDNA have a different function. We will discuss the role of two ISA subunits in starch biosynthesis in developing barley endosperm.
