title: [On the complex formation of proteins with cu ions under acidic conditions].
abstract: In order to determine the influence of copper additives on the protein digestibility, the complex formation of proteins with Cu ions under acidic conditions (pH=2.2) was investigated. Isolated soja-protein (300 mg) resp. pepsin was mixed with 10 mumol (2.49 mg) CuSO4-5H2O and dialysed against low molecular complexing agents with increasing affinity towards copper ions. The experiments with soja-protein showed, that most of the Cu ions dialysed (97% of total Cu2+ content) without any addition of complexing agents, pepsin, however, had a lower percentage (83% of total Cu2+ content). The remaining copper ions in pepsin could only be removed by alanin and ammonium-tetramethylendithiocarbamate. Therefore it is concluded, that in the acidic range Cu ions only form complexes with pepsin, but not with soja-protein. This effect is due to the very low isoelectric point of pepsin. The determination of iron, nickel, and zinc in native proteins revealed, that at pH=2.2 iron and nickel are stronger linked to pepsin than to soja-protein; only zinc was loosely bound to both proteins.
mesh_terms: D003300:Copper; D003956:Dialysis; D004063:Digestion; D005503:Food Additives; D010434:Pepsin A; D010940:Plant Proteins; D011506:Proteins; D013025:Glycine max; D014131:Trace Elements
chemical_list: D005503:Food Additives; D010940:Plant Proteins; D011506:Proteins; D014131:Trace Elements; D003300:Copper; D010434:Pepsin A
vernacular_title: Zur Komplexbildung von Proteinen mit Cu2+-Ionen im sauren Milieu