Faculty of Bioresource Science, Akita Prefectural University, Shimoshinjo-Nakano, Akita-City 010-0195, Japan.
Faculty of Bioresource Science, Akita Prefectural University, Shimoshinjo-Nakano, Akita-City 010-0195, Japan.
Plant Sci. 2014 Jul;224:1-8. doi: 10.1016/j.plantsci.2014.03.021. Epub 2014 Apr 5.
The present study was conducted to characterize the functions of the major starch synthase (SS) isozymes SSI, SSIIa, and SSIIIa in rice endosperm and their functional interaction with starch branching enzyme (BE), by using their purified recombinant proteins. All the SS isozymes had similarly significant activities toward branched glucans such as amylopecin and glycogen whereas they scarcely showed activities toward maltohexaose. In vitro studies indicate that SSI mainly attacked A and B chains with degree of polymerization (DP) of 6 and 7 in their external segments and elongated them to DP8. It is likely that SSIIa and SSIIIa produced wider ranges of intermediate chains and long chains, respectively. This study also revealed that without addition of exogenous primer, the glucan synthesis of SSI in the presence of ≧0.3 M citrate was accelerated by the addition of any of the rice BE isozymes- BEI, BEIIa, or BEIIb, whereas no such interaction occurred between SSIIa or SSIIIa with any of the BEs. The SSI-BE unprimed glucan synthesis absolutely required citrate. The interaction between SSI and BE was established by stimulation of SSI activity with BE and by activation of the BE activity by SSI.
本研究旨在利用纯化的重组蛋白表征水稻胚乳中主要淀粉合酶（SS）同工酶 SSI、SSIIa 和 SSIIIa 的功能及其与淀粉分支酶（BE）的功能相互作用。所有 SS 同工酶对支链葡聚糖（如直链淀粉和糖原）均具有相似的显著活性，而对麦芽六糖的活性则很低。体外研究表明，SSI 主要攻击 A 和 B 链，其外部片段的聚合度（DP）为 6 和 7，并将其延长至 DP8。SSIIa 和 SSIIIa 可能分别产生更广泛的中间链和长链。这项研究还表明，在不存在外源引物的情况下，在存在≥0.3 M 柠檬酸的情况下，添加任何一种水稻 BE 同工酶（BEI、BEIIa 或 BEIIb）均可加速 SSI 的葡聚糖合成，而 SSIIa 或 SSIIIa 与任何 BE 之间均未发生这种相互作用。SSI-BE 无引物葡聚糖合成绝对需要柠檬酸。SSI 和 BE 之间的相互作用是通过 BE 刺激 SSI 活性以及 SSI 激活 BE 活性来建立的。
