Stimulation of reduced lysozyme regeneration by transferrin and lactoferrin

Human serum transferrin, bovine lactoferrin, and hen conalbumin were investigated with respect to the ability of the bound metal to catalyze thiol oxidation. All three proteins were able to stimulate the oxidation of thiols in both reduced lysozyme and reduced glutathione. The efficiency of the metal in catalyzing thiol oxidation was not decreased by binding to transferrin, suggesting that transferrin-bound metals are completely available to both low and high molecular weight thiols. A 5 × 10^?7m concentration of transferrin isolated from serum was able to catalyze the formation of 70% of the theoretical lysozyme activity from reduced inactive lysozyme by 60 min. Increased rates of lysozyme activity formation were observed with copper-saturated transferrin. Decreased lysozyme regeneration rates were observed with the iron-saturated molecule compared to native transferrin. The results presented suggest that metalloproteins may aid in the maintenance of the steady-state cellular concentrations of low molecular weight disulfide by catalyzing the autooxidation of thiols.