On the Restriction of the Rotational Diffusion of Proteins in Polymer Networks

The rotational relaxation time of dansyl‐labelled human serum albumin in solutions of dextran and polyethylene glycol of high concentrations (up to 0.3 g/ml) has been determined by fluorescence depolarization measurements. The increase in relaxation time due to the impeding effect of the polymer chains is moderate and the relaxation time is approximately doubled in 0.25 g/ml of polymer. The effect is independent of the molecular weight of the polymer; sucrose has approximately the same effect as dextran. It is concluded that, in contrast to the very restricted translational diffusion, the rotational diffusion of the albumin molecule is only moderately suppressed, even in very dense polymer networks.