北蕉葉酪胺酸與p-cresol之動力學分析

A Kinetic Analysis of p-cresol Oxidation by Banana Leaf Tyrosinase

本研究擬北蕉（Giant Cavendishii，AAA）葉所含酪胺酸酶為材料，探討其與單酚類基質p-cresol作用產生遲滯期（lag phase）之動力學關係。北蕉葉之粗抽液經硫銨分劃後進行動力學分析，發現影響遲滯期主要因素有酵素與基質濃度、pH值、添加微量雙酚以及基質配位基之位置特異性；在酵素濃度高、基質濃度低時會使遲滯期時間縮短；於pH 5.5時之遲滯期最短；添加微量雙酚也會造成遲滯期縮短之現象，以p-cresol為基質時分別添加L-DOPA（L-dihydroxyphenylalanin）、catechol獲得Kact（雙酚活化常數）分別為4.45μM、1.74μM；得知雙酚不同也會影響遲滯期長短，而且L-DOPA雙酚活化單酚酶能力低於catechol；另外基質取代基位置差異亦會影響遲滯期長短，使用othro-、mata-、para-等不同氯取代位置cholrophenol當基質時，發現遲滯期時間由短至長順序為p-、o-、，m-，同時發現香蕉葉酪胺酸酶可作用具有毒性的氯酚化合物。經由本研究可了解農業廢棄物香蕉葉中所含的酪胺酸酶作用p-cresol的遲滯期與動力學機制並得知其對單酚基質具有廣特異性，期待將這些特性應用於工業合成及廢水處理。

This kinetic analysis of p-cresol by tyrosinase was investigated in this study. The tyrosinase used in this study was extracted from the leaf of banana （Giant Cavendishii, AAA） and partially purification by ammonium sulfate fractionation. The activity was determined by a lag period, that duration depended on the monophenol and its concentration, as well as enzyme concentration, pH, and the presence of catalytic amounts of diphenol. Moreover, the lag phase decreased with increasing diphenol concentration, it was possible to evaluate Kact, the activation diphenol constant, which showed a value of 4.45μM toward L-DOPA and 1.74μM for catechol. Substitution of chlorine at different position of phenol was exhibited different hydroxylation rate with an order of para＞ortho＞meta. The results from this study indicates that banana leaf tyrosinase exhibit wide substrate specificity toward monophenol, making its potential in medical and industry.