Zaborsky O R, Ogletree J, Hou C T
Biochim Biophys Acta. 1975 Mar 28;386(1):18-25. doi: 10.1016/0005-2795(75)90241-x.
The circular dichroism spectrum of protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa has been examined in the absence of the substrates, protocatechuic acid and O-2 and in the presence of the competitive inhibitors, protocatechualdehyde and p-hydroxybenzoic acid. The native enzyme has a low alpha-helical content (less than 1%) and exhibits several positive ellipticity bands between 250 and 300 nm (255,269,275 and 292 nm) and two, low intensity, negative bands at 330 and 480 nm. In the presence of protocatechuic acid and the absence of O-2, spectral changes are evident in the side chain and visible regions. There is a shift in the aromatic-region maximum from 275 to 267 and in the visible region from 330 to 348 and from 480 to 555 nm. No spectral changes are observed upon the removal or addition of only O-2. Different spectral changes in both the side chain and visible regions are observed in the enzyme with the two competitive inhibitors under either aerobic or anaerobic conditions. The spectral changes observed in the side chain region suggest the possible participation of aromatic residues in the binding process, but it is not yet established as to whether these residues play an active or passive role in binding and/or catalysis.
在不存在底物原儿茶酸和O₂以及存在竞争性抑制剂原儿茶醛和对羟基苯甲酸的情况下，对铜绿假单胞菌原儿茶酸3,4-双加氧酶的圆二色光谱进行了研究。天然酶的α-螺旋含量较低（小于1%），在250至300 nm之间呈现出几个正椭圆率带（255、269、275和292 nm），在330和480 nm处有两个低强度的负带。在存在原儿茶酸且不存在O₂的情况下，侧链和可见区域的光谱变化明显。芳香区域的最大值从275 nm移至267 nm，可见区域从330 nm移至348 nm以及从480 nm移至555 nm。仅去除或添加O₂时未观察到光谱变化。在有氧或无氧条件下，用两种竞争性抑制剂处理的酶在侧链和可见区域均观察到不同的光谱变化。在侧链区域观察到的光谱变化表明芳香族残基可能参与了结合过程，但这些残基在结合和/或催化中是起主动还是被动作用尚未确定。
