Translational motion of hydration water on protein surface

In the study of the role of the hydration water in the structure and function of biosystems, one of the major problems is the investigation of the dynamics of hydration water. For this purpose, many papers were reported about relaxation measurements of hydration water by 1HNMR. Most of them were concerned with rotational motion of hydration water. There were few papers dealing with translational motion of hydration water in rigid systems, such as unfrozen water and bound water of protein. The spin-echo or pulse gradient methods are useless in the study of such systems, whereas the self-diffusion coefficient D, the index of translational motion, can be estimated by the spin-locking method. This report is concerned with the study of the translational motion of unfrozen and bound water of solution and powder of protein, respectively, and the measuring of the values of D by spin-locking using of 1HNMR. The coefficient can be obtained by measuring the relaxation time T1 varying the locking power w1. For hydration monolayer in protein solution at -35 degrees C, D values of 10(-9)-10(-10) cm2/sec, and for monolayer in protein powder at room temperature, D values of 10(-10)-10(-11) cm2/sec were obtained. By heat denaturation of the protein, the values were slightly altered, though the rotational motion revealed by T1 measurement appeared not so affected. This difference might derive from the alteration of the protein surface by the unfolding of protein molecule due to the denaturation.(ABSTRACT TRUNCATED AT 250 WORDS)