l-Histidine enhances stability of hemoglobin concentrates by coordinating with free iron

The objective of this investigation was to evaluate the effects of l -histidine on the stability of porcine hemoglobin concentrates during storage. The results indicated that the addition of l -histidine increased the oxyhemoglobin content and a* values but decreased the methemoglobin content and free iron content (P   <   0.05) during storage. The addition of iron cation decreased both the oxyhemoglobin content and a* values but increased both the methemoglobin content and free iron concentration (P   <   0.05). CD spectra revealed that the free iron content induced the transformation of the hemoglobin secondary structure from an α-helix (close structure) to a β-pleated, β-turn, and random coil arrangement (loose structure), while l -histidine weakened this behavior of the free iron. Infrared spectra demonstrated that the l -histidine coordinated with the free iron (Fe 2   + or Fe 3   + ) to give the corresponding complex at 25   °C and pH   7.3. Therefore, l -histidine enhanced the stability of hemoglobin concentrates by coordinating with free iron.