The isoelectric point of serum-globulin as determined by kataphoresis

Following the determination of the isoelectric point of insulin by kataphoretic methods (Howitt and Prideaux, 1932) it appeared to the authors that a similar determination for serum-globulin would be of interest owing to the globulin-like character of insulin. A comparison between the kataphoretic behaviours of these two proteins which are physiologically so different would also be afforded. Previous determinations of the isoelectric point of serum-globulin have generally been based on methods of maximum insolubility, or coagulation. Thus Kugelmass (1922) obtained a value of pH 4·55, whilst Krebs (1925), employing the coagulative action of proteins on a gold sol, found pH 5·4. The experiments of Rona and Michaelis (1910, 1927) gave the value 5·44 in close agreement with that of Krebs. Reiner (1927), however, has stated that serumglobulin has a broad isoelectric zone and is not a homogeneous substance. The findings of this worker are probably explained by the conclusions of Svcdberg and Sjögren (1928) that serum-globulin is a chemical entity, which degradated into fractions during normal treatment, such as “salting-out” with ammonium sulphate.