Sutherland G R, Khindaria A, Chung N, Aust S D
Biotechnology Center, Utah State University, Logan 84322-4705, USA.
Biochemistry. 1995 Oct 3;34(39):12624-9. doi: 10.1021/bi00039a018.
It has recently been discovered that lignin peroxidase isozyme H2 (LiPH2) has the ability to oxidize Mn2+ (Khindaria et al., 1995). Furthermore, at pH 4.5, the physiological pH of Phanerochaete chrysosporium, LiPH2 oxidizes Mn2+ at a much faster rate (25 times) than veratryl alcohol (VA). The ability of Mn2+ to act as a redox mediator for indirect oxidations catalyzed by LiPH2 was therefore investigated. In the presence of physiologically relevant levels of oxalate and Mn2+, the rate of LiPH2-catalyzed oxidation of all substrates studied was dramatically increased. Up to 10-fold stimulations were observed compared to the rates of oxidation of substrate in either the presence or absence of VA. We propose that the stimulation is due to the ability of LiPH2 to oxidize Mn2+, producing the strong oxidant Mn3+, at a high rate. The rates of oxidation of the substrates showed a hyperbolic dependence on Mn2+ in the presence of oxalate, a chelator which was required for maximal activity. The oxalate dependence of the oxidation rates correlated well with the concentration of the 1:1 complex of Mn(2+)-oxalate. The relative concentrations of the substrates and H2O2 and the rate constants for their reactions with Mn3+ determined which chemical was oxidized by the enzymatically produced Mn3+. The importance of the ability of Mn(2+)-oxalate to stimulate the oxidation of chemicals by LiPH2 is discussed.
最近发现木质素过氧化物酶同工酶H2（LiPH2）具有氧化Mn2+的能力（Khindaria等人，1995年）。此外，在黄孢原毛平革菌的生理pH值4.5下，LiPH2氧化Mn2+的速度比藜芦醇（VA）快得多（25倍）。因此，研究了Mn2+作为LiPH2催化间接氧化的氧化还原介质的能力。在存在生理相关水平的草酸盐和Mn2+的情况下，所研究的所有底物的LiPH2催化氧化速率显著增加。与在有或没有VA的情况下底物的氧化速率相比，观察到高达10倍的刺激。我们认为这种刺激是由于LiPH2能够快速氧化Mn2+，产生强氧化剂Mn3+。在草酸盐存在下，底物的氧化速率对Mn2+呈双曲线依赖性，草酸盐是最大活性所需的螯合剂。氧化速率对草酸盐的依赖性与Mn(2+)-草酸盐1:1络合物的浓度密切相关。底物和H2O2的相对浓度以及它们与Mn3+反应的速率常数决定了哪种化学物质被酶促产生的Mn3+氧化。讨论了Mn(2+)-草酸盐刺激LiPH2氧化化学物质的能力的重要性。
