Starch-biosynthesis enzymes producing the less stickiness of boiled rice of indica variety

与粳稻品种相比，籼稻品种的米饭粘性较低，这可能是由于籼稻支链淀粉的长链含量较高。因此，我们研究了来自籼稻和粳稻品种的水稻胚乳的分支酶，因为该酶在涉及淀粉生物合成的酶中可能具有产生短链和非常长链的支链淀粉的重要作用。在所研究的6个籼、粳稻品种中，西开184具有典型的籼型支链淀粉，而西开194具有少量的极长支链的粳稻型支链淀粉。经凝胶电泳后活性染色检测，在授粉后20天左右的未成熟胚乳中，赛开184和赛开194至少有两种不同数量的分支酶同工酶。通过丁基-Toyoproxin 650 S、DEAE-Sepharose FF、Mono Q、Superose 12和直链淀粉-Sepharose 6 B层析纯化主要异构体，使其基本上不含淀粉酶。通过磷酸化酶刺激试验和分支连接试验测定，两种制剂显示出相似的活性比率，并且发现当它们与还原直链淀粉作为底物孵育时，优先转移长链。这种类型的链转移类似于玉米BE-I同种型，但不同于玉米BE-II同种型和菜豆酶，优先转移短链。然而，水稻同种型和玉米BE-I在产生相对高量的具有d的链方面不同。p. 10-12 and of a chain with d.第6页，分别。这一结果可能意味着这种内在的链转移作用决定了植物来源的支链淀粉的链长分布。进一步研究淀粉合成酶和/或分支酶的催化功能，可能有助于阐明籼稻米饭粘性较低的原因。

Boiled rice of indica variety is less sticky compared with that of japonica variety, being suggested to be due to a higher amount of very long chains of indica amylopectin. Therefore, we examined branching enzyme from rice endosperm of indica and japonica varieties because the enzyme, out of enzymes involving starch biosynthesis, may have an important role to produce short and very long chains of amylopectin. Among six varieties examined here of indica and japonica rices, Saikai 184 variety had a typical type of indica amylopectin and Saikai 194 had that of japonica amylopectin having a small amount of very long chains. Immature endosperms (about 20 days after pollination) of Saikai 184 and Saikai 194 had at least two isoforms of branching enzyme with a various amount when examined by activity staining after gel electrophoresis. A major isoform was purified to be essentially free of amylase by chromatography on butyl-Toyopearl 650S,DEAE-Sepharose FF,Mono Q,Superose 12 and amylose-Sepharose 6B.Both preparations showed a similar ratio of the activities determined by the phosporylase stimulation assay and the branch linkage assay, and were found to transfer preferentially long chains when they were incubated with reduced amylose as a substrate. This type of chain transfer resembled that for maize BE-I isoform, but differed from that for maize BE-II isoform and for kidney bean enzyme which preferentially transferred short chains. However, the rice isoform and maize BE-I differed in producing a relatively high amount of chains with d. p. 10-12 and of a chain with d. p. 6, respectively. This result might imply that such an intrinsic chain transfer action determines chain-length distribution of amylopection in plant origin. The less stickiness of indica boiled rice might be clarified by further experiments on catalytic functions of starch synthase and /or minor isoform of branching enzyme.