Reduction of Ferrylmyoglobin by β-Lactoglobulin

Abstract

Reduction of iron (IV) in ferrylmyoglobin in the presence of P-lactoglobulin in aqueous solution is the result of two parallel reactions: (i) a so-called autoreduction, and (ii) reduction by β-lactoglobulin in a second-order-reaction resulting in bityrosine formation in β lactoglobulin. In the pH-region investigated (5.4–7.4), the rate of reduction increased for both reactions with decreasing pH. The second order-reaction had for non-denatured β-lactoglobulin the activation parameters: AH* = 45 kJ.mol^-1 and AS^* = -93J mol^-1.K^-1 at pH = 7.0 and ionic strength 0.16 (NaCl). Reduction of ferrylmyoglobin by β-lactoglobulin denatured by heat (86°C for 3 min) or by hydrostatic pressure (300 MPa for 15 min) resulted in formation of higher molecular weight species as detected by size-exclusion chromatography and by SDS-PAGE. No molecular weight changes were observed for reduction of ferrylmyoglobin by native P-lactoglobulin. Detection of bityrosine in the native β-lactoglobulin fraction after oxidation with ferrylmyoglobin indicated intra-molecular bityrosine formation. In heat-denatured β-lactoglobulin bityrosine formation could be of intra-molecular and/or of inter-molecular origin, the latter being confirmed by size- exclusion chromatography.

Key Words:

• Ferrylmyoglobin
• β-lactoglobulin
• cross-linking
• bityrosine