Determination of correlation times modulating NMR relaxation times in some protein and enzyme solutions using T1/T2 rate

In the present work, using 64 MHz (1.5 Tesla) MR spectrometer, 1/T1 (Spin-Lattice) and 1/T2 (Spin-Spin) Relaxation rates in H2O of solutions of Hemoglobin and three enzymes (Pepsin, Protease and ?-chymotrypsin) were investigated versus concentration at room temperature. The relaxation rates in the D2O and H2O/D2O (0.1ml H2O+0.9ml D2O) solutions of Hemoglobin were also studied versus concentration and temperature at 400 MHz (9.4 Tesla) NMR spectrometer.The 1/T1 and 1/T2 relaxation rates at 64 MHz increase linearly with concentrations of Hemoglobin and the enzymes. The 1/T1 and 1/T2 determined at 400 MHz also increase linearly with concentration of Hemoglobin. The temperature dependence of the Hemoglobin solution at 400 MHz showed that 1/T1 and 1/T2 relaxation rates increase linearly when the temperature increases.The correlation time (?) modulating relaxation mechanism was calculated for each of high magnetic field (9.4 Tesla) and low magnetic field (1.5 Tesla) by using theory derived in this thesis. The ? values at 64 MHz were 2.0017ns for Hemoglobin, 5.3225ns for Pepsin, 2.2865ns for Protease and 3.8398ns for ?-chymotrypsin. In addition, the ? values for D2O and H2O/D2O solutions of Hemoglobin at 400 MHz were 1.22ns and 1.27ns, respectively. The data showed that T1/T2 relaxation rates can be used for the accurate calculation of ? values when proteins and enzymes were assumed to be spherically symmetrical.The present results obtained for protein and enzymes suggest that the relaxation rates are caused by dipolar interaction modulated by molecular tumbling. The fast chemical exchange of protons between free and bound water is also involved in the process.Keywords: 1/T1 spin-lattice relaxation rate, 1/T2 spin-spin relaxation rate, 64 MHz MR, 400 MHz NMR, ? correlation time, dipolar interaction, hemoglobin, pepsin, protease, ?-chymotrypsin.