• 作者： 蘇仲卿; 宋賢一; 鄭麗麗; 楊兆鸞; 謝慶晃
• 作者服務機構： Department of Agricultural Chemistry National Taiwan University; and Institute of Biological Chemistry; and Institute of Zoology; Academia Sinica
• 中文摘要： 一、根據穩態動力學分析，同位素交換，平衡透析及產物阻害作用等研究結果，推論香蕉果實蔗糖合成酵素所催化反應的反應機構如下：(1)反應機構為異構化非連續型（即isoping-pong bi bi機構），就蔗糖分解方向而言，與酵素第一個結合的基質為蔗糖，最後離開酵素的基質為UDPG. (2)JE 0.02至0.2mM範圍內，UDP為正協同性異位控制劑。在此濃度範圍外，UDP的Hill氏係數都滅少，在高濃度下，甚至於變成負數，(3)在高濃度下（〉50mM），蔗糖阻害此一酵素作用。（’）此一酵素的自由型，具有F與G部位，可供基質結合“有果?基的醣（如蔗糖）或果糖本身，及有葡萄?基的化合物（如蔗塘及UDPG），各分別可與F和G部位結合。G部位依兩種方式和葡萄?基結合；一為非共價鍵式的低親和性結合，另一為依分子內轉?基方式產生的共價鍵結合，產生E-G或EG：UDP複台物之後，酵素分子發生異構化作用，構成一種接受尿核?酸化台物中尿核?基的新部位（U∣部位）。 二、自蒼白化豌豆幼芽的芽軸，子葉及根部得到的蔗糖合成異構酵素閒，具有免疫交叉反應性。
• 英文摘要： I. Based on the data obtained from extensive steady-state kinetic ana-lyses, isotope exchange，equilibrium dialysis and product inhibition stu-dies, the kinetic mechanism of the reaction catalyzed by the sucrose syn-thetase purified from banana fruits was elucidated as following：（1）Thereaction proceeds according to an iso-nonsequential (iso ping pong bi bi)mechanism. In the direction of sucrose cleavage, the enzyme binds withsucrose first and release UDPG last。(2) UDP is a positive cooperativeallosteric effector within a concentration range of 0.02-0.2 mM. At higheror lower concentration, the Hill coefficient of this substrate decreases andeven reaches a negative value at the higher concentration range. (3) Su-crose at higher concentrations（>50 mM) is inhibitory. (4) The enzymein the free state has F and G sites open for substrate binding, and sub-strates with a fructosyl residue (sucrose) or fructose and those with a glu-cosyl residue (sucrose and UDPG) are capable of binding with F and Gsites, respectively。The G sites accept glucosyl residues in two ways: oneis low affinity, non-covalent type and the other a covalent type formedby intramolecular transglucosylation。After the formation of E-G or E-G·UDP complex, the enzyme undergoes isomerization and a new site (U-site) for binding with uridyl compounds through their uridine ends iscreated。 II·Sucrose synthetase isozymes obtained from the epicotyls，cotyledonsand roots of etiolated pea seedlings are immunologically cross reactive·
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