Biochemistry p. 8899 - 8913 (2011)
Update date:2022-08-03
Topics:
MacHonkin, Timothy E.
Doerner, Amy E.
PcpA is an aromatic ring-cleaving dioxygenase that is homologous to the well-characterized Fe(II)-dependent catechol extradiol dioxygenases. This enzyme catalyzes the oxidative cleavage of 2,6-dichlorohydroquinone in the catabolism of pentachlorophenol by Sphingobium chlorophenolicum ATCC 39723. 1H NMR and steady-state kinetics were used to determine the regiospecificity of ring cleavage and the substrate specificity of the enzyme. PcpA exhibits a high degree of substrate specificity for 2,6-disubstituted hydroquinones, with halogens greatly preferred at those positions. Notably, the kcat app/KmAapp of 2,6-dichlorohydroquinone is ~40-fold higher than that of 2,6-dimethylhydroquinone. The asymmetric substrate 2-chloro-6-methylhydroquinone yields a mixture of 1,2- and 1,6-cleavage products. These two modes of cleavage have different K mO2app values (21 and 260 μM, respectively), consistent with a mechanism in which the substrate binds in two catalytically productive orientations. In contrast, monosubstituted hydroquinones show a limited amount of ring cleavage but rapidly inactivate the enzyme in an O2-dependent fashion, suggesting that oxidation of the Fe(II) may be the cause. Potent inhibitors of PcpA include ortho-disubstituted phenols and 3-bromocatechol. 2,6-Dibromophenol is the strongest competitive inhibitor, consistent with PcpA's substrate specificity. Several factors that could yield this specificity for halogen substituents are discussed. Interestingly, 3-bromocatechol also inactivates the enzyme, while 2,6-dihalophenols do not, indicating a requirement for two hydroxyl groups for ring cleavage and for enzyme inactivation. These results provide mechanistic insights into the hydroquinone dioxygenases.
View MoreNINGXIA DARONG CHEMICALS & METALLURGY CO.,LTD.
Contact:86-952-2179751
Address:Darong Road, Dawukou, Shizuishan, Ningxia 753001, China
Hangzhou Hysen Pharma co.,Ltd.
website:http://www.hysenpharma.cn/
Contact:0086-571-88298791
Address:#701,Gudun Road Hangzhou
Contact:+86-731-84427351
Address:154 JIANXIANG SOUTH ROAD
Hangzhou Maytime Bio-Tech Co.,Ltd.
website:http://www.maytime.com.cn
Contact:+86-571-88925295 88920965
Address:NO.2-1701 Ganghui Central Ningwei Street, Xiaoshan Hangzhou Zhejiang China
Contact:86-511-85210668 0511-85210668, 85210818, 85210898
Address:Yihai Garden E-902,NO.99 Daxi RD., Zhenjiang Jiiangsu ,China
Doi:10.1021/jo01287a104
(1967)Doi:10.1039/c39950002315
(1995)Doi:10.1016/j.phytochem.2010.06.011
(2010)Doi:10.1021/jo00382a035
(1987)Doi:10.1007/BF00996508
()Doi:10.1016/0223-5234(96)88298-5
(1995)