A STUDY OF THE BROWNIAN DYNAMICS OF BOVINE SERUM-ALBUMIN BY PROTON RELAXATION

The nonselective relaxation times T-1 and T-2 of protons of bovine ser um albumin in heavy-water solutions were measured at three resonance f requencies: 10.8, 27, and 90 MHz; and various temperatures, pH, and io nic strengths. The data obtained were interpreted in terms of our earl ier model, according to which the motion of a protein molecule in solu tion can be separated into three types of motion: the internal local m otions, the Brownian rotation of a molecule as a whole, and the slowes t motion owing to the mutual orientation of protein molecules caused b y intermolecular electrostatic interactions. A comparative analysis of the dynamic parameters of lysozyme, ribonuclease A, binase, tryptopha n repressor, and bovine serum albumin was performed. The measurements of T-1 and T-2 at various pH and ionic strengths provided for a qualit ative explanation of the effect of the intermolecular Coulomb repulsio n between charged protein molecules on their rotational diffusion para meters.