Naidja A, Liu C, Huang P M
Department of Soil Science, University of Saskatchewan, 51 Campus Drive, Saskatoon, Saskatchewan, S7N 5A8, Canada.
J Colloid Interface Sci. 2002 Jul 1;251(1):46-56. doi: 10.1006/jcis.2002.8349.
Limited information is available on formation chemistry of enzyme-Mn oxide complexes. Adsorption isotherm of protein molecules (tyrosinase) on birnessite (delta-MnO(2)) at pH 6.0 and room temperature (23 degrees C) was of H type, indicating a very high affinity of the enzyme protein molecules to the birnessite mineral surfaces. After thorough washing of the protein-mineral complex with deionized-distilled water, up to 89% of adsorbed protein molecules remained bound to the mineral surfaces. When a high amount of the protein was immobilized, the X-ray diffractogram shows a significant decrease in the intensity of characteristic d-spacings of birnessite. No shift to higher values of the d-spacings of protein-birnessite complex was observed, indicating that the enzyme molecules were not intercalated in the mineral structure but immobilized at the external surfaces and the edges of the mineral oxide. By comparison to the free enzyme, infrared absorption spectra of the protein-birnessite complexes show a shift by up to 11 cm(-1) to lower frequencies in the absorption bands characteristic of amide I and II modes of the polypeptides chains. The mineral surfaces exerted some strain on the protein structure, resulting in an alteration of the protein molecular conformation after binding to the mineral colloid surfaces. In the free state, the globular protein molecules had a spheroid shape with an average cross-sectional diameter of 70+/-6 nm. The unfolding and flattening of the protein molecules after immobilization is clearly shown in atomic force micrographs. Compared to the tyrosinase-birnessite complex, similar FTIR spectra and atomic force micrographs were observed for the pure protein, bovine serum albumin (BSA), after immobilization on birnessite. The information obtained in this study is of fundamental significance for understanding birnessite as an adsorbent of biopolymers and the catalytic role of the enzyme-birnessite complex.
关于酶 - 锰氧化物复合物的形成化学，目前可用信息有限。在pH 6.0和室温（23℃）下，蛋白质分子（酪氨酸酶）在水钠锰矿（δ - MnO₂）上的吸附等温线为H型，表明酶蛋白分子对水钠锰矿矿物表面具有非常高的亲和力。用去离子蒸馏水彻底洗涤蛋白质 - 矿物复合物后，高达89%的吸附蛋白质分子仍与矿物表面结合。当大量蛋白质被固定时，X射线衍射图显示水钠锰矿特征d间距的强度显著降低。未观察到蛋白质 - 水钠锰矿复合物的d间距向更高值的移动，这表明酶分子没有插入矿物结构中，而是固定在矿物氧化物的外表面和边缘。与游离酶相比，蛋白质 - 水钠锰矿复合物的红外吸收光谱显示，在多肽链酰胺I和II模式的特征吸收带中，频率向低频方向移动了高达11 cm⁻¹。矿物表面对蛋白质结构施加了一些应变，导致蛋白质与矿物胶体表面结合后分子构象发生改变。在游离状态下，球状蛋白质分子呈球形，平均横截面直径为70±6 nm。原子力显微镜图像清楚地显示了固定后蛋白质分子的展开和平坦化。与酪氨酸酶 - 水钠锰矿复合物相比，固定在水钠锰矿上的纯蛋白质牛血清白蛋白（BSA）观察到了类似的傅里叶变换红外光谱和原子力显微镜图像。本研究中获得的信息对于理解水钠锰矿作为生物聚合物吸附剂以及酶 - 水钠锰矿复合物的催化作用具有重要的基础意义。
