STRONG AND WEAK BINDING OF WATER TO PROTEINS STUDIED BY NMR TRIPLE-QUANTUM FILTERED RELAXATION SPECTROSCOPY OF O-17-WATER

The triple-quantum filtered (TQF) spin-echo signal of O-17-water, in t he presence of proteins, was analysed to yield estimates of the number of weakly, and strongly bound water molecules. The analysis used a co nstrained direct iterative regression procedure with a three-state mod el of fast-exchange. Thus, the population size of free, weakly, and st rongly bound water were determined simultaneously. The two fractions o f the bound water were estimated by using correlation time(s) estimate d in other studies. Bovine serum albumin (BSA), basic pancreatic tryps in inhibitor (BPTI), lysozyme and oxyhaemoglobin were studied. Of the four proteins, BSA contained the largest number of strongly and weakly bound water molecules, there being similar to 30 of the former and si milar to 3000 of the latter under conditions of high protein concentra tion. The correlation time of the proteins increases with their concen tration in solution, and when this was taken into account for BSA the estimated number of strongly bound water molecules did not change sign ificantly. This NMR technique, and data analysis, will probably also b e useful in studies of water binding and mobility in various systems i ncluding hydrogels, protein networks, membranes, cells and tissues. (C ) 1997 Elsevier Science B.V.