[Protein isolation by means of complexing agents. 2. Formation of insoluble complexes of sunflower albumins with alginate or pectin]. / Proteingewinnung unter Einsatz von komplexbildenden Stoffen. 2. Mitt. Zur Bildung unlöslicher Komplexe zwischen Sonnenblumenalbuminen und Alginat bzw. Pektin.

The formation of insoluble complexes of sunflower seed albumin and alginate or pectin is studied by means of turbidimetric titration and by determining the pH-dependent precipitability of protein. The complex formation that is based on electrostatic interaction is a function of the pH value and the protein-polyanion ratio. Consequently, it is affected by the neutral salt content of the solutions. 90% and more of the dissolved protein may be precipitated if the proportion of the precipitant amounts to 20%. A sodium chloride content of 0.6% reduces the precipitability by alginate to 74%. In the presence of 0.3% sodium chloride, at most 55% of protein are still precipitated by pectin. The difference in strength between the albumin-alginate and the albumin-pectin complex is also expressed by the dye-binding power. Albumin-pectin complexes bind the same amount of amido black as free protein. On the contrary, albumin-alginate complexes exhibit reduced dye-binding power due to stronger binding of the protein to the polyanion. The results obtained by turbidimetric titration of model systems can, in principle, be extrapolated to the precipitation of albumins from protein extracts. In accordance with the heterogenicity of the protein, the turbidimetric titration of the albumin-alginate and the albumin-pectin complexes exhibits two maxima.

[Alkali treatment of proteins. I. Behavior of sulfhydryl and disulfide groups in alkali-treated beta-lactoglobulin and alpha-lactalbumin]. / Zur Alkalibehandlung von Proteinen. 1. Mitt. Das Verhalten der Sulfhydryl- und Disulfidgruppen in alkalibehandeltem beta-Lactoglobulin und alpha-Lactalbumin.

The alkali treatment of beta-lactoglobulin and alpha-lactalbumin results in the splitting of disulphide bonds in the protein molecules. When a 0.8-10(4) M beta-lactoglobulin solution in a 0.022 N sodium hydroxide solution (pH = 12) is heated at 90 degrees C for 30 min, 0-4 M disulphide groups, 2.2 M sulfhydryl groups and 1.8 M sulphide ions/M dimeric beta-lactoglobulin are detectable of the total of 4 M disulphide groups and 2 M sulfhydryl groups/M dimeric beta-lactoglobulin. The sulphide ions can be determined directly in the form of hydrogen sulphide or by calculating the difference between the values from the amperometric-argentometric titration and those from the method of ELLMAN (reaction with DTNB). The disulphide groups are determined with the aid of DTNB after reduction with sodium borohydride. The sulfhydryl groups obtained by reduction with sodium borohydride re-oxidize, the reaction velocity being of the second order. If the disulphide groups are reduced with sodium borohydride, the argentometric-amperometric determination of the sulfhydryl groups by means of the platinum rotating-disk electrode is disturbed by the presence of boric acid.

[Modification of proteins by reaction with carbonyl compounds]. / Modifizierung von Proteinen durch Reaktion mit Carbonylverbindungen

The authors deal with chemical and physico-chemical changes in casein and vegetable globulins after reaction with aldehydes or acylation with carboxylic acid chlorides and anhydrides. The stepwise blocking of the alpha- and epsilon-amino groups leads to modified proteins with lowered isoelectric points and changes in the solubility and precipitability characteristics and in the electrophoretic behaviour. There are relationships between the relative nutritive value (as determined by means of Tetrahymena pyriformis) and the blocking of lysine. On acylation of the protein, the relative nutritive value is influenced by the length of the acyl residue and the kind of modification (N or O-blocking).