• 作者： 宋賢一
• 作者服務機構： 國立臺灣大學農業化學系
• 中文摘要： 為了暸解豌豆芽子葉，芽軸及根三部分蔗糖合成酵素之作用機構，將暗條件下培養之豌豆芽分為三部分加以抽取純化至不含蔗糖轉化酵素後，研究其飽和曲線，先以雙倒數作圖法分析蔗糖分解作用之動力學後，以第二次作圖法求得子葉，芽軸及根的酵素對蔗糖的Km值分別為0.072, 0.074及0.568 M, 對UDP則分別為0.246, 0.074及0.214 mM,子葉酵素對UDP的飽和曲線的sigmoidicity高而對蔗糖的則低，但芽軸及根的酵素則相反。沒有第二個基質存在的情形下，各部分豌豆芽酵素都可與蔗糖或UDPG結合，並可催化蔗糖與C一果糖之間的同位素交換，而UDP可加強交換速率及量，此等結果與動力學的數據皆證實所有豌豆芽蔗糖合成酵素都依ping-pong bi bi機構催化反應。 由所得各種結果知豌豆芽的各部分含有控制作用不同的異構酵素(lsozymes)存在，而其特性適台於在異化作用強的子葉中催化蔗糖的合成而在同化作用強的芽軸及根中催化UDPG的合成。
• 英文摘要： Sucrose synthetases purified from cotyledons, epicotyls and roots ofetiolated pea seedlings are compared in their kinetics and the reactionmechanism. The kinetic parameters of the sucrose synthetases in thedirection of sucrose degradation reaction were measured. From the secondaryplots, the Km values for sucrose were determined to be 0.072, 0.074 and0.568 M for cotyledon, epicotyl and root enzymes, respectively. The Kmfor UDP were 0.246, 0.074 and 0.214 mM for cotyledon, epicotyl and rootenzymes, respectively. The sigmoidicity of the cotyledon enzyme in theUDP saturation curve was high and that in the sucrose saturation curvewas low, while for epicotyl and root enzymes the reverse was true. In the absence of the second substrate, enzymes can bind with sucroseor UDPG. The enzymes also catalyze the isotope exchange between sucroseand C-fructose and UDP enhances the rate and amount of exchange.These and kinetic data indicate that a ping-pong bi bi mechanism is operablefor all pea sucrose synthetases. All the available data establish the presence of isozymes in differentparts of pea seedlings and reveal their properties suitable for catalyzingthe synthesis of sucrose in the catabolic cotyledon but the synthesis of UDPGin the anabolic epicotyl and root.
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