肽链长度对La3＋与微过氧化物酶相互作用的影响

为了了解稀土元素与酶相互作用的化学机理, 用紫外-可见(UV-Vis)吸收光谱技术和电化学方法研究了La^3＋与过氧化物酶(POD)的模型化合物, 微过氧化物酶-8 (MP-8)或微过氧化物酶-11 (MP-11)的相互作用机理. La^3＋优先与MP-8或MP-11分子中血红素卟啉环上的2个丙酸基团的羰基氧发生键合作用, 使它们的聚集程度降低, 卟啉环的非平面性增加. 由于MP-8分子聚集的倾向要小于MP-11, La^3＋使MP-8聚集程度的降低和卟啉环非平面性增加的程度要大于MP-11. 由于MP-11的肽链较长而能形成螺旋状构象, 使肽链上的羰基基团被包埋在肽链的疏水基团中, 因此, La^3＋与MP-11中肽链上的羰基氧基本上不能发生键合作用. 而MP-8的肽链较短, 不能形成螺旋状结构, La^3＋也能与肽链上的羰基氧发生键合作用.

Effect of Peptide Length on Interaction between La3+ and Microperoxidase

In order to understand the chemical mechanism of the interaction of the enzymes with the rare earth elements, the mechanism of the interaction between La3 and the model of POD, MP-8 or MP-11 was studied using UV-Vis absorption spectroscopy and electrochemical technique. It was found that La3 was bound firstly to the carbonyl oxygen of the metacetonic acid group in the heme group of the MP-8 or MP-11 molecule, resulting in the decrease of their aggregation extents and the increase of the non-planarity of the porphyrin group. The decrease extent of the aggregation of the molecules and then the increase extent of the nonplanarity of the porphyrin group for MP-8 due to La3 binding were greater than those for MP-11 be-cause the aggregation tendency of MP-8 was less than that of MP-11. The peptide of MP-11 was long enough to form the helical conformation, thus, the carbonyl oxygen in the peptide would be embedded in the hydrophobic microenvironment of the peptide, and La3 was not easy to coordinate with the carbonyl oxy-gen in the peptide of MP-11. However, the peptide of MP-8 was relatively short, it could not form the helical conformation and therefore, La3 was easy to interact with the carbonyl oxygen in the peptide of MP-8.