Yoshihara S, Tatsumi K
Arch Biochem Biophys. 1986 Aug 15;249(1):8-14. doi: 10.1016/0003-9861(86)90554-0.
To characterize the properties of diphenyl sulfoxide (DPSO) as a new type of electron acceptor for guinea pig liver aldehyde oxidase (AO), we compared the kinetics of the reductions of DPSO and other classical electron acceptors such as O2 and ferricyanide. The double-reciprocal plot of the 2-hydroxypyrimidine (2-OH PM)-linked DPSO reduction with the highly purified enzyme was biphasic. Similar biphasic plots were obtained with the reductions of other electron acceptors. Only the lower Km value, which was obtained by extrapolation of the plot at lower concentrations of 2-OH PM, was identical with that shown by the freshly prepared crude enzyme. DPSO as well as menadione progressively inhibited the reductions of O2 and ferricyanide with time. Menadione inhibited the DPSO reduction noncompetitively with respect to 2-OH PM and competitively with respect to DPSO, while its mode of inhibition of ferricyanide reduction was uncompetitive for either the electron donor or the acceptor. On the other hand, DPSO showed an uncompetitive and a noncompetitive inhibition of ferricyanide reduction with respect to 2-OH PM and ferricyanide, respectively. These results may indicate that DPSO interacts with the enzyme at the same site as menadione, and thereby when other electron acceptors are present it serves as an actual inhibitor rather than as an electron acceptor for AO.
为了表征二苯亚砜（DPSO）作为豚鼠肝脏醛氧化酶（AO）新型电子受体的特性，我们比较了DPSO与其他经典电子受体（如O2和铁氰化物）还原反应的动力学。用高度纯化的酶进行2-羟基嘧啶（2-OH PM）偶联的DPSO还原反应的双倒数图呈双相。其他电子受体的还原反应也得到了类似的双相图。只有通过在较低浓度的2-OH PM下外推该图获得的较低Km值与新鲜制备的粗酶所显示的值相同。DPSO以及甲萘醌随着时间的推移逐渐抑制O2和铁氰化物的还原。甲萘醌对2-OH PM而言非竞争性抑制DPSO的还原，对DPSO而言竞争性抑制其还原，而其对铁氰化物还原反应的抑制模式对电子供体或受体而言均为非竞争性。另一方面，DPSO对2-OH PM和铁氰化物而言分别对铁氰化物还原反应表现出非竞争性和非竞争性抑制。这些结果可能表明DPSO与甲萘醌在酶的同一部位相互作用，因此当存在其他电子受体时，它作为AO的实际抑制剂而非电子受体。
