The main component of the water-soluble proteins of wheat flour has been isolated in sufficient quantity for chemical and physical characterisation. This was achieved by a combination of ion-exchange chromatography on carboxymethyl cellulose and gel filtration through Sephadex G75. The protein isolated was judged to be 90% pure by zone electrophoresis. Sedimentation analysis yielded a single symmetrical peak with an S"ZO,W value of 2.45. The molecular weight was found to be 19,300 by gel filtration, and the diffusion coefficient estimated by the same method was 10.47 x A molecular weight of 16,000 was calculated from sedimentation equilibrium analysis in a dissociating medium. The ultra-violet spectrum of the isolated albumin exhibited a maximum at 278 nm and from this an E : z value of 13.1 was calculated. No free sulphydryl groups could be detected. Amino acid analysis showed that this protein has a composition similar to those of other soluble wheat-flour preparations. A molecular weight of 16,300 was calculated from the amino acid analysis. End-group analysis of the protein showed that serine is the N-terminal amino acid. The C-terminal amino acid was found to be resistant to release by both carboxypeptidase A and carboxypeptidase B.
IntroductionIn early work with wheat proteins, fractions isolated by solubility properties were used, and all such fractions have been shown to be grossly heterogeneous. Heterogeneity of the flour proteins soluble in water and dilute salt solution has been demonstrated by a number of workers.1-6 Ionexchange chromatography on DEAE-cellulose has been used for the isolation of several components from the dilute-salt extracts of flour by a number of investigators5s7 while a few components of the water-soluble fraction of flour have been isolated by small-scale preparative starch-gel electrophoresis8 or by a combination of gel filtration and starch-gel electrophore~is.~ In most cases, the amount of homogeneous protein isolated was insufficient for extensive characterisation studies, although amino acid analysis and molecular weight determinations' and N-terminal amino acid analysislo have been reported for some.In earlier work,g the major protein component of the water-soluble fraction of flour was isolated as an electrophoretically homogeneous component by a combination of gel filtration through Sephadex GlOO and small-scale preparative starch-gel electrophoresis. However, only small quantities could be isolated by this procedure and means of effecting the isolation of this protein in larger amounts were sought. Since separation by charge differences as effected by starch-gel electrophoresis was an essential step in the isolation, it appeared that other methods of separation based on charge differences might be effective.The present paper describes the application of ion-exchange chromatography on carboxymethyl (CM) cellulose in combination with gel filtration through Sephadex G75 for the isolation of a major albumin of the water-soluble fraction of wheat flour. Sufficient quantities...
