Isolation and partial characterization of the acalin A and B fraction of cottonseed globulins

Abstract

The cottonseed globulins account for the majority of the protein in the mature cottonseeds. Previous attempts to purify and characterize these proteins have resulted in techniques for fractionating the globulins into two classes termed acalin A and B. These techniques were used to prepare the native acalin A and B protein isolates from four different varieties and species of cottonseeds. They were characterized with regard to amino acid composition, optical rotary dispersion, immunological response, weight average molecular weight of the native acalin A complex, and the interaction of acalin A with concanavalin A. As shown by the SDS-gel electrophoresis, both of the protein isolates are complex mixtures containing numerous polypeptides. Techniques were developed for the isolation of the individual polypeptides after they had been denatured with SDS. This involved preparative electrophoresis for the acalin A polypeptides by a procedure which utilized a unique method to nondestructively identify the location of the polypeptide in the acrylamide gel matrix. The acalin B polypeptides were isolated by recycling permeation chromatography on columns packed with controlled pore glass and by permeation chromatography with a two-column system packed with Ultrogel. The purified polypeptides were characterized with regard to molecular weight, amino acid composition, presence of disulfide bonds, and possible identity of some polypeptides as glycoproteins.