Acid treatment of a light‐petroleum extract of barley flour yielded two proteins (termed hordothionins) closely similar in electrophoretic behaviour to the purqthionin doublet obtained from wheat by the same procedure. The major (faster) component, hordothionin a has been obtained apparently pure. Comparison of its amino acid composition, peptide maps, immunological reactions and C‐terminal end group with those of purothionin a has confirmed the relationship between the proteins from the two genera although some differences in amino acid composition and sequence have been found. Extraction of barley flour with buffered saline followed by acid treatment yielded proteins with similar properties to the hordothionins; this supports previous observations on the relationship between the purothionins and their corresponding globulins.
Purothionin, an unusual wheat protein and the ‘fast‐moving wheat globulins’ have been separated into two components. Earlier evidence of the close similarity of purothionin and these ‘globulins’ is strengthened by amino acid analyses, ‘fingerprints’ (peptide mapping) and C‐terminal end group determination of the individual components. A preparation similar to the crude ‘lipoprotein’ precursor of purothionin previously reported in the literature and stated to contain ‘lecithin’ on the basis of the presence of lipid phosphorus has been partially resolved into six components, and the presence of phosphatidyl choline, amino phospholipids and two glycolipids has been demonstrated in fractions containing purothionin.
1. Three very similar proteins, each of approx. 120 amino acid residues but lacking phenylalanine and histidine, were isolated from wheat (Triticum aestivum) flour in sufficient quantities for further structural studies. 2. Each protein, after reduction and carboxymethylation, was cleaved at the three methionine residues with CNBr to give four major peptides, which were isolated. These peptides are suitable for future sequencing studies, as the sums of their amino acid compositions are in good agreement with those of the whole proteins. 3. The N- and C-terminal peptides were identified. 4. Evidence from amino acid analyses, N-terminal amino acids and electrophoretic mobilities of the peptides suggests a high degree of homology between the proteins. Definite differences in C-terminal amino acids and the number of glycine, alanine and arginine residues were found in the C-terminal peptides.
Three wheat proteins, CMl, CM2 and CM3 constituting in total more than 1 % of flour proteins, have been isolated from chloroform-methanol (2 : 1 v/v) extracts of flour. CMl and 2 have single chains with m.w. of 13 000 and isoleucine as the C-terminal amino acid. They appear to be closely related even in amino acid sequence as judged from fingerprints. All three proteins are soluble in chloroformmethanol after freeing from lipid, but only moderately so in water. CM3 becomes insoluble after reduction of S S bonds due to aggregation of the reduced polypeptide chains by secondary forces. It differs appreciably from CMl and 2 in sequence and has C-terminal leucine and a m.w. of 15 000.ThemobilitiesofCM2and3 at pH3.2areveryclose to ALB 13AandALB 13B, respectively, and the albumins found in electrophoretic patterns of crude gliadin preparations do in fact represent mixtures of both classes.
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