- 作者： 曾德賜; 陳瑞祥; 李敏惠
- 作者服務機構： 國立中興大學植物病理學系
- 中文摘要：
本研究旨在探討由甲硫胺酸所衍生的自由基在甲硫胺酸與核黃素混合物(MR)光動微生物毒性中所扮演的角色。利
用電子順磁共振光譜儀，於pH4.00的MR中可恆定地測得分屬羥基自由基與甲基自由基所特有之DMPO-OH‧quartet共
振訊號及DMPO-CH3‧sextet共振訊號；且此兩種自由基之同時形成端視甲硫胺酸於系統中之添加。當以已知致死效果
較差之作用基質如半胱胺酸、色胺酸、及酥胺酸等取代甲硫胺酸參與反應時，反應過程中所偵測到的主要產物則為超氧
自由基而非羥基自由基，且反應中亦無法測得甲基自由基之產生。添加已知可增強MR微生物毒性之超氧歧化酵素（su-
peroxide dismutase)時，反應中羥基自由基明顯減少，伴隨之甲基自由基的量則明顯增加。添加同樣可促進MR微生物
毒性之抗壞血酸及過氧化氫時，則此兩自由基之產生量均有明顯增加。相反的，添加對MR毒性有明顯減低作用的硫?
(thiourea)及desferal時，則此兩自由基之產生量均明顯受到抑制。綜合本研究結果顯示，由甲硫胺酸所衍生的甲基自由
基的產生常伴隨羥基自由之形成，且與MR之微生物毒性有關，其應為MR光動毒性中不容忽視的關鍵因子。
c - 英文摘要： The role of methionine-mediated free radical production in the photodynamic microbial toxicity ofmethionine-riboflavin mixture (MR) was determined. For MR at pH 4.0, a quartet signal of DMPO-OH· anda sextet signal of DMPO-CH3·, characteristic of hydroxyl and methyl radicals, respectively, were consistentlydetected by electron spin resonance (ESR) spectroscopy. The concomitant production of both radical specieswas dependent on the presence of methionine and riboflavin. Replacement of methionine by cysteine, tryp-tophan, or tyrosine, substrates known to be less toxigenic as compared to methionine, led to production ofmainly superoxide rather than hydroxyl radical wherein the methyl radical was not detected. Addition ofsuperoxide dismutase, an agent known to enhance the microbial toxicity of MR, led to a reduction of thequartet signal, but the amplitude of the sextet signal increased. The addition of ascorbic acid (1 mM) or H2O2(1000 ppm), the other known toxicity enhancing supplements, as a contrast, increased the formation of bothhydroxyl and methyl radicals. Furthermore, the addition of thiourea or desferral, agents known to reduce themicrobial toxicity of MR, led to diminishment of both free radicals. The results clearly indicated that theproduction of methionine-mediated methyl radical was a phenomenon closely associated with hydroxyl radi-cal formation and the known microbicidal activity. It thus appeared to be an indispensable factor contributingto the photodynamic toxicity of MR.
- 中文關鍵字： ESR spectroscopy; methionine riboflavin mixture; hydroxyl radical; methyl radical; photody- namic toxicity.
- 英文關鍵字： --
