Proteins obtained from agricultural sources were blended with divalent metal ions to see if binding reactions occurred between protein chains. Feather keratin, egg albumin, and wheat gluten showed elastic modulus increases of 2-3 times with addition of divalent transition metal ions Cu2+ and Zn2+. Increasing concentrations of ions resulted in increased stiffness. Birefringence experiments performed concurrently with tensile experiments showed refractive index changes indicative of network formation. Binding divalent alkaline earth metal Ca2+ ions did not result in an elastic modulus increase. Addition of Zn2+ to egg albumin resulted in a 34% decrease in water permeability but no change in oxygen permeability. FTIR spectroscopy showed that the directed valence of the transition metals was primarily binding glycerol and amide sites on the protein and secondarily carbonyl sites on the protein. (C) 2007 Wiley Periodicals, Inc.