Factors determining starch function and molecular structure; how characteristic is enzymes of starch synthesis in plant origin

为了找出植物起源中淀粉特性的决定因素，我们研究了1)高直链淀粉的分子结构和功能，2)颗粒结合淀粉合成酶（GBSS）的数量与直链淀粉含量的关系，3)分支酶（BE）的功能与支链淀粉结构的关系。结果表明，GBSS和BE在淀粉1的表征中起重要作用。我们发现两个高直链淀粉品种的淀粉与普通大麦品种具有相似的直链淀粉和支链淀粉分子结构，实际上是高直链淀粉，与籼稻不同，糊化非常困难。采用SDS-PAGE法测定了大麦（4个品种）、水稻（12个品种）、小麦（6个品种）、玉米（2个品种）和马铃薯（5个品种）淀粉中GBSS含量的变化规律。(1)两种植物的GBSS含量与实际直链淀粉含量之间存在一定的关系。大麦和玉米直链淀粉含量随GBSS用量的增加而增加。水稻、小麦和马铃薯的直链淀粉含量随GBSS添加量的增加而保持不变。(2)合成直链淀粉的水稻GBSS也可能拉长部分支链淀粉链，产生类似直链淀粉的超长链。从大麦胚乳（开花23天后）中纯化BE。支链淀粉有两种异构体（BE I和BE II），它们在链传递中具有不同的功能，主要异构体BE I被认为是确定支链淀粉短链分布的主要异构体。

In order to find out the determining factor of starch characteristic in plant origin, we examined 1) molecular structure and function of high-amylose starches, 2) the relation between amount of granule bound starch synthase (GBSS) and amylose content and 3) the relation between function of branching enzyme (BE) and amylopectin structure. The results obtained suggested that GBSS and BE played an important role in characterization of starch.1. We found that starches from two high-amylose cultivars of barley had similar molecular structures of amylose and amylopectin to a normal cultivar of barley, and were actually high-amylose, differing from in the case of indicia rice, and gelatinized with very difficulty.2. We determined GBSS amount of starches from barley (4 cultivars), rice (12 cultivars), wheat (6 cultivars), maize (2 cultivars) and potato (5 cultivars) by SDS-PAGE, and found the following relations on GBSS amount. (1) Two types of plants were found in terms of the relation between GBSS amount and actual amylose content. One type of plant was barley and maize in which amylose content increased with increase of GBSS amount. The other type was rice, wheat and potato in which amylose content was constant even with increase of GBSS amount. (2) Rice GBSS, which synthesizes amylose, might also elongate a part of amylopectin chains and produce amylose-like very long chains.3. BE was purified from barley endosperm (23 days later flowering). There were two isoforms (BE I and BE II), which had different function in chain transfer, and the main isoform, BE I, was suggested to determine short-chain distribution of amylopectin.