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).

In den in der vorliegenden Arbeit beschriebenen Versuchen wurde die selektive Acylierung der Hydroxy‐ und Aminogruppen von Casein vorgenommen und der Nährwert der Acylderivate mit Hilfe des Testorganismus Tetrahymena pyriformis abgeschätzt. Es wurde gezeigt, daß die Acylierung der Hydroxygruppen den Nährwert des Eiweißes nicht herabsetzt, während die Acylierung der Aminogruppen diese Kennziffer wesentlich verringert. Die Acylierung mit langkettigen Fettsäuren erhöht den Nährwert des Eiweißes unabhängig von der Acylierungsrichtung.

Studies on a monosubstrate system (pepsin - substrate) yielded values which characterize pepsin digestion as a multi-stage process. During the first stage, pepsin hydrolyzes the most accessible parts of the protein molecule, i.e., those portions of the peptide chains which are situated on the surface of the globule. During the stage of apparent cessation of the reaction, very few peptide bonds are hydrolyzed which are essential for the formation of the tertiary structure. After hydrolysis of these bonds, the inner parts of the globule become accessible, the hydrolysis of which proceeds more slowly.

No abstract