The precipitation of enzymes from cell extracts of Saccharomyces cerevisiae by polyethyleneglycol.

The equilibrium precipitation by polyethyleneglycol of alcohol dehydrogenase, fumarase and invertase from Saccharomyces cerivisiae has been studied. The precipitation can often be represented by a simple linear equation analogous to Cohn's equation for salting-out: log S = X-a x C where S is the protein solubility and C the concentration of polymer, X and a are constants. A more complex form of the equation log S + fS = X-a x C where f is a protein self-interaction coefficient, is sometimes necessary, particularly at high protein concentrations and at pH values distant from the isoelectric point. Protein solubility with respect to polyethyleneglycol is influenced by temperature and ionic strength and particularly by pH and protein concentration. Different results were obtained by discrete and sequential addition of polyethyleneglycol. Effective fractional separation of the enzymes is restricted to protein concentrations below about 10 mg/ml.