Lippmaa E T, Olivson A I, Iarvet Iu I-Kh, Aguraĭuia R K
Mol Biol (Mosk). 1983 May-Jun;17(3):484-92.
The study of internal mobility in enzymes is of considerable importance for the understanding of their catalytic function, which cannot be adequately described as a property of a rigid protein. [13C]NMR spectroscopy permits simultaneous and selective observation of spectral lines from carbon atoms in many different residues in the enzyme with the chemical shift and relaxation parameters sensitive to structure, conformation and local motion. The changes in internal mobility in bovine carbonic anhydrase B (carbonate hydrolase, EC 4.2.1.1) in the native form and at various stages of denaturation are studied. Measurements of the relaxation parameters (T1, T1 rho) and of the NOE of 13C nuclei in the native protein showed that the extensive beta-sheet together with groups in the active center has a considerable internal librational mobility with tau G about 10(-11) s. This librational mobility is fairly uniform for all the alpha-carbons in the native enzyme. The use of a semiempirical modification of the motional theory proposed by Woessner allows to use simultaneously all the relaxation parameters measured in order to determine reliable values of the various correlation times.
研究酶的内部流动性对于理解其催化功能具有相当重要的意义，因为酶的催化功能无法简单地用刚性蛋白质的性质来充分描述。[13C]核磁共振光谱能够同时且选择性地观测酶中许多不同残基的碳原子的谱线，其化学位移和弛豫参数对结构、构象和局部运动敏感。本文研究了天然状态下以及变性各个阶段的牛碳酸酐酶B（碳酸水解酶，EC 4.2.1.1）的内部流动性变化。对天然蛋白质中13C核的弛豫参数（T1、T1ρ）和核Overhauser效应（NOE）的测量表明，广泛的β-折叠结构以及活性中心的基团具有相当大的内部摆动流动性，其相关时间τG约为10^(-11)秒。对于天然酶中的所有α-碳原子，这种摆动流动性相当均匀。使用对Woessner提出的运动理论进行的半经验修正，能够同时利用所测量的所有弛豫参数来确定各种相关时间的可靠值。
