• 作者： 李平篤; 蘇仲卿
• 作者服務機構： 國立臺灣大學農業化學系
• 中文摘要： 就水稻穀實（臺南五號品系）在成熟過程中蔗糖轉變為澱粉之生化機構進行研究，所得主要結果如下：
  以〔U－ C〕葡萄糖與〔6－ H〕果糖的等分子混合物及以酵素方法合成的葡萄?基和果?基分別以　C和　H標幟的
  雙標示放射性蔗糖（Double-labeled radioactive sucrose）為基質與不同成熟期的水稻穀實，然後分離並追?測定　C
  和 H在醣磷酯（Sugar phosphate），醣核?酸（Sugar nucleotide）及澱粉之分布比例，得知在乳熟期水稻穀實中蔗糖
  分子之葡萄?基比果?基為更直接而優良的澱粉合成前體（以蔗糖為基質時，澱粉中的　C-葡萄?與 H-葡萄?分子比數
  高於5，但如果以兩種單醣的混合物為基質，則此比數約為1），表示蔗糖經過蔗糖合成?（Sucrose synthetase）催化產
  生的尿核?二磷酸葡萄糖（UDPG）與腺核?二磷酸葡萄糖（ADPG）均可直接被利用於澱粉生合成。由蔗糖產生的葡萄
  糖1-磷酯（GIP）與其他己醣6-磷酯相似具有極低的　C-與 H-六碳醣分子比例（約0.3以下），但尿（腺）核?二磷酸葡
  葡糖則與澱粉一樣具有相當高的放射性分佈比例（4以上），此一實驗結果亦可證明尿（腺）核?二磷酸葡萄糖和葡萄糖1
  -磷酯之間並無平衡關係存在，換言之尿核?二磷酸葡萄不一定需要經由焦磷解?（Pyrophosphorylase）以葡萄糖1-磷
  酯為中間體先轉變為腺核?二磷酸葡萄糖，再以之合成澱粉。
  為了與上述放射性基質給與試驗配合加強印證，特別將水稻自開花後至成熟期間定期測定重要化學成分，如可溶性蛋
  白、總蛋白、澱粉、還原性與非還原性糖類及水分等含量之變化，同時，也測定了與蔗糖轉變為澱粉有關之酵素活性，如
  轉化?（Invertase）蔗糖合成?（Sucrose Synthetase），尿（腺）核?二磷酸葡萄糖焦磷解?〔UDPG（ADPG）－Py-
  rophosphorylase〕，己醣動化?（Hexokinase）及葡萄糖磷酸異位?（Phosphoglucomutase）等之消長情形。
• 英文摘要： Rice grains at different stages of maturation were fed with double-labeled sucrose ( C-glucosyl- H-fructoside) or an equimolar mixture of U- C-glucose and 6- H-fructose; and the incorporation of C and H into sugar phosphates, sugar nucleotides and starch were analyzed. From the results, it wasconcluded that during the early stage of seed development, sucrose synthetase is the key enzyme forsucrose-starch transformation, and the UDP(ADP)glucose produced directly from sucrose may be used asthe precursor of starch synthesis. The molar ratio of C/ H in glucose 1-P was similar to that of hexose6-P (less than 0.3) while the molar ratios of C/ H in ADPglucose and UDPglucose were as high as thatin starch (over 5). These results indicate that glucose 1-P is not in equilibrium with ADPglucose andUDPglucose, eliminating the possibility of UDPglucose pyrophosphorylase-ADPglucose pyrophosphorylasecatalyzed conversion of UDPglucose into ADPglucose via glucose 1-P as the intermediate in the sucrose-starch transformation pathway. The data were augmented with the measurements of the levels of soluble and total proteins, starch,reducing and nonreducing sugars and the changes in activities of enzymes involved in the transformation ofsucrose into starch, such as invertase, sucrose synthetase, UDP(ADP)glucose pyrophosphorylase, hexokinaseand phosphoglucomutase in maturing rice grains during the 4 weeks after flowering. Results in supportof the conclusion derived from the radiotracer feeding experiments were obtained.
• 中文關鍵字： --
• 英文關鍵字： --