• 作者： 蘇仲卿
• 作者服務機構： 臺灣大學農學院農業化學系生物化學研究室; 中央研究院生物化學研究所
• 中文摘要： 本篇綜合報告以放射性同位素追?方法及酵素性質的探討，研究植物中蔗糖代謝所得到的一些結果。
  給與以 C標幟的單醣於竹筍的實驗結果顯示外加的單醣迅速經過蔗糖磷酸合成?及蔗糖磷酸水解?所催化反應系統
  被合成為蔗糖，而蔗糖轉化?對於蔗糖異化代謝的貢獻有限。為進一步研究蔗糖異化代謝，合成了雙標幟蔗糖（葡萄?基
  以 C，果?基以 H標幟），以其對充實中稻穀及豌豆與綠豆幼芽進行給與實驗。另一方面以 C-葡萄糖及 H-果糖的
  等分子混合物進行實驗，做為蔗糖經過水解後代謝過程的探測。結果顯示自由的葡萄糖及果糖被同化為聚醣的比率約略相
  等，但是蔗糖分子內的葡萄?基被利用於聚醣合成的比率遠大於果?基。這種結果表示蔗糖合成?所催化自蔗糖與核?二
  磷酸反應而產生的糖核?酵為聚醣合成所使用前體的主要來源。又自稻穀分離得到的糖核?酸（UDPG與ADPG） C/
  H比數遠大於葡萄糖1磷酸（GIP），表示在稻穀中並無由UDPG焦磷解?與ADPG焦磷解?共同作用而進行的UDPG
  轉糖基於ADPG的作用發生。另一實驗顯示乳熟期稻穀中有充分的蔗糖合成?活性可提供澱粉合成活性於澱粉合成活性。
  自許多植物材料純化了可直接自蔗糖合成UDPG的蔗糖合成?及間接自蔗糖水解物合成UDPG的UDPG焦磷解?兩
  種酵素而研究了其性質，其中對蔗糖代謝有明顯意義者亦於本文中予以討論。
  y
• 英文摘要： This paper summarizes the results of tracer feeding experiments and enzyme studies aimed at theelucidation of sucrose metabolic nathways in higher plants. The results of feeding C-labeled monosaccharides into bamboo shoots indicated that the external-ly administered monosaccharides were efficiently converted into sucrose via sucrose 6'-phosphate synthase-sucrose 6'-phosphate phosphatase pathway and invertase played only a minor role in sucrose metabolism.A double labeled sucrose ( C-glucosyl- H-fructoside) was synthesized and utilized in the elucidation ofsucrose-polysaccharide transformation pathways in rice grains and seedlings of pea and mungbean. Anequimolar mixture of C-glucose and H-fructose was used as the control to check the pathway viainvertase. The results indicated that free glucose and fructose were transformed into polysaccharides withequal opportunities but the glucosyl moiety of sucrose had a transformation rate much higher than thatof the fructosyl moiety. These findings indicate that sucrose synthase catalyzed sugar nucleotide formationfrom sucrose and nucleoside diphosphate served as the major route of Precursor supply in polysaccharidesynthesis. The great anrerence in C/ H ratios found for sugar nucleotides (ADPG and UDPG) and GIPruled out the possibility of UDPG pyrophosphorylase and ADPG pyrophosphorylase catalyzedUDPG-ADPG transformation in the starch synthesizing rice grain system. In the milky stage rice grains,enough sucrose synthase activity was present to provide a saturating amount of precursors for starchsynthase activity. The two UDPG forming enzymes sucrose synthase (directly from sucrose) and UDPG pyrophos-phorylase (indirectly from sucrose via invertase catalyzed hydrolysis) were purified from various plantmaterials and some of their properties relevant to sucrose metabolism in plants were discussed.
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