Lanir A, Gradstajn S, Navon G
Biochemistry. 1975 Jan 28;14(2):242-8. doi: 10.1021/bi00673a008.
Longitudinal and transverse proton relaxation rates of water in solutions of manganese(II) bovine carbonic anhydrase have been measured by pulsed nuclear magnetic resonance spectrometry as a function of temperature (2-35 degrees), frequently (5-100 MHz) and pH. The pH dependence of the longitudinal relaxation rate was fitted to a sigmoidal curve with a pK value at 7.8, while the esterase activity of the manganese(II) enzyme in the hydrolysis of p-nitrophenyl acetate revealed an inflection point at pK = 8.2. The hydration number of manganese(II) carbonic anhydrase could be derived using either the frequency dependence of T1p or the T1p/T2p ratio at only one (high) frequency. Both treatments are in agreement with a model in which one water molecule is bound to the metal at high pH. At low pH the relaxation data imply that no-H20 exists in the first coordination sphere of the manganese ion. The various parameters which are responsible for the proton relaxation mechanisms have been evaluated and are compared to other manganese(II) enzyme systems. The pH dependence of the binding constant of manganese to apocarbonic anhydrase is also reported.
通过脉冲核磁共振光谱法，测量了锰（II）牛碳酸酐酶溶液中水的纵向和横向质子弛豫率，作为温度（2 - 35摄氏度）、频率（5 - 100兆赫兹）和pH值的函数。纵向弛豫率的pH依赖性拟合为一条S形曲线，其pK值为7.8，而锰（II）酶在对硝基苯乙酸水解中的酯酶活性在pK = 8.2处出现拐点。锰（II）碳酸酐酶的水合数可以通过仅在一个（高）频率下使用T1p的频率依赖性或T1p/T2p比值来推导。两种处理方法都与一个模型一致，即在高pH值下一个水分子与金属结合。在低pH值下，弛豫数据表明锰离子的第一配位层中不存在水分子。对负责质子弛豫机制的各种参数进行了评估，并与其他锰（II）酶系统进行了比较。还报道了锰与脱辅基碳酸酐酶结合常数的pH依赖性。
