1H NMR relaxation measurements in highly concentrated water protein solutions

Measurements performed on biological systems, such as parts of plants, seeds and animals reveal non-exponential decay of the spin-spin relaxation function. Such behaviour has also been observed in the eye lens, which is a relative simple system mainly built from water, 65% of total weight, and 35% organic material, mainly structural proteins. To understand this phenomena one has to find a simplified system which will allow measurement and description of magnetic relaxation processes and compare them to the biological system. One such system can be water solution of bovine serum albumin (BSA) with concentration higher than 30%. It was found that nuclear magnetic relaxation time, T-2, in aqueous solution of albumin for low concentration depends mainly on fast proton exchange between free water and water adsorbed on the protein surface. For higher concentration of BSA (30%-55%) a second proton exchange process starts to play a role and in consequence the spin-spin relaxation function is a sum of two exponential functions. Copyright (C) 1999 John Wiley & Sons, Ltd.