A study of a series of recombinant fungal laccases and bilirubin oxidase that exhibit significant differences in redox potential, substrate specificity, and stability
详细信息 查看全文
- 作者：Feng ; Xu ; Shin ; Woonsup ; Brown ; Stephen H. ; Wahleithner ; Jill A. ; Sundaram ; Uma M. ; Solomon ; Edward I.
- 关键词：Laccase ; Redox potential ; Kinetics ; Stability ; Bilirubin oxidase ; Fungus
- 刊名：Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular Enzymology
- 出版年：1996
- 出版时间：February 8, 1996
- 年：1996
- 卷：1292
- 期：2
- 页码：303-311
- 全文大小：882 K
文摘
A series of fungal laccases (Polyporus pinsitus, Rhizoctonia solani, Myceliophthora thermophila, Scytalidium thermophilum) and one bilirubin oxidase (Myrothecium verrucaria) have been studied to determine their redox potential, specificity, and stability. Polyporus andRhizoctonia laccases possess potentials near 0.7-0.8 V (vs. NHE), while other oxidases have potentials near 0.5 V. It is observed that higher redox potential correlates with higher activity. By EPR, no significant change in the geometry of type 1 copper (II) site is observed over this series. At the optimal pH, the two substrates studied, 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid) and syringaldazine, show Km values ranging from 10 to 120 and from 1 to 45 μM; and kcat values ranging from 50 to 16000 and 200 to 3000 per min, respectively. The enzymes are more stable in the neutral-alkaline pH range. The thermal stability is in the order of bilirubin oxidase Myceliophthora laccase Scytalidium laccase > Polyporus laccase > Rhizoctonia laccase. Based on these results and the sequence alignments made against Zucchini ascorbate oxidase it is speculated that structural differences in the substrate-activation site (a ‘blue’, type 1 copper center) control the redox potential range as well as substrate specificity, and the cystine content contributes to stability.