Analysis of the proteins of rat serum by starch electrophoresis and by cationic detergent analysis. I. Identification of an unusual globulin.

A protein of unusual characteristics has been identified in normal rat sera by electrophoretic separation at pH 8.6, followed by precipitation of each fraction with a cationic detergent. This protein, which is closely identified with albumin after electrophoresis at pH 8.6, precipitates with cationic detergent at a low pH in contrast to albumin which precipitates with detergent only at a high pH. This protein has characteristics of a globulin and is designated as a "fast alpha fraction." This fraction and albumin are present in about equal amounts in sera of normal rats. A separation of the fast alpha fraction can be made by electrophoresis in an acetate buffer of pH 4.25 and by precipitation according to a modified Cohn, cold-alcohol technique. A protein of similar characteristics has not been found in either human or rabbit sera studied by the same method of electrophoresis and subsequent sub-fractionation with cationic detergent.