Binding of iron by chicken muscle protein digests: the size of the iron-binding peptides

Abstract

The dilute salt-insoluble proteins (DSIPs) were extracted from chicken muscle and digested in the presence of ferric iron. The size of the peptides was determined by ultrafiltration using membranes with various molecular weight cut-offs (MWCOs). Over 90% of the peptides in both the pepsin and pepsin–pancreatin digestions were smaller than 10 kDa and more than 45% were smaller than 3.5 kDa. Pancreatin digestion increased the amount of small peptides (<3.5 kDa) as compared to pepsin digestion alone. Most of the iron was in a form too large to pass the 10 kDa MWCO membrane and was presumably bound to a few large peptides. About 10% of the iron was smaller than 3.5 kDa, but there was very little in the intermediate range (3.5–10 kDa). Pancreatin digestion produced more soluble iron than pepsin alone, but the size distribution was similar for both digestions. The smaller peptides (<10 kD) bound very little iron during digestion but could bind iron if separated from the large peptides before iron addition. The large iron-binding peptides were separated by ultrafiltration, and a 22-fold increase in specific activity (iron mg−1 peptide) was achieved using a 10 kDa MWCO membrane. © 2000 Society of Chemical Industry