Kinetics of protein agglomeration. A nephelometric method for the determination of total protein in biological samples.

The kinetics of agglomeration of proteins precipitating in a viscous solution was measured by light scattering. The resulting transitory maximum was linearly proportional to the mass of protein over three orders of magnitude. The change in scattering intensity is described as a change in scattering symmetry due to a continuous increase in particle size. This method is both fast (minutes) and sensitive (30 ng protein) and is independent of the chemical composition of the different protein species and is barely influenced by size and shape of the proteins. By solubilising the protein samples in an alkaline dodecyl sulfate solution this method can be applied to all types of biological samples (e.g. tissue homogenates, membrane proteins) and also to all types of biological preparations containing detergents as well as urea, sucrose, salts and lipids.