The interaction of ascorbic acid with hemoglobin: Relevance to hemin release and lipid peroxidation.

The interactions between L-ascorbic acid (i.e., Vitamin C, VC) and bovine hemoglobin (Hb) were comprehensively analyzed using fluorescence, circular dichroism, UV-vis absorption spectra and molecular docking method, to elucidate the structural mechanisms through which VC altered Hb redox states and stabilities. VC interacted with the central cavities of Hb to form Hb-VC complex via static quenching mechanism involving nonradiative energy transfer, with van der Waals forces and hydrogen bonds playing predominant roles in the binding processes. VC was surrounded by residues such as α1-Thr137, α1-Ser138, α1-Tyr140 and α1-Arg141 residues. After that, the binding of VC would narrow the crevices near the heme domain of Hb, which converted ferric (met-) Hb to ferrous (oxy-) Hb and deoxy-Hb state and suppressed hemin liberation (level of free hemin was 4.35 µM (Hb alone) and 2.77 µM (Hb-VC complex)). Moreover, VC significantly inhibited Hb-catalyzed lipid peroxidation in liposome and washed muscle, which was probably due to the conversion to oxy-Hb state and reduced dissociation of hemin (not free iron). In accordance with its effects on Hb redox states and stability, VC effectively maintained the red color of hemeprotein during the storage. Altogether, the attenuation of free hemin release from Hb molecule represents a new mechanism towards the anti-oxidant capacity of VC in Hb-containing foods.