Structural characterization and stability analysis of phosphorylated nitrosohemoglobin

Abstract

Phosphorylation modification by sodium tripolyphosphate (STP) on nitrosohemoglobin (NO-Hb) and its effect on the protein structure and stability were studied. Phosphate groups were found to bridge to NO-Hb via C–O–P bonds through serine and tyrosine residues. Hydrothermal treatment with STP maintained the α-helix stability of NO-Hb, and this change in secondary structure improved the proteins stability. Compared to NO-Hb, phosphorylated NO-Hb (P–NO-Hb) was more stable with respect to light (outdoor light, indoor light, and dark conditions), oxidant (hydrogen peroxide), high temperature, and non-neutral pH. The absorbance of P–NO-Hb was nearly twice those of Hb and NO-Hb (P < 0.05), and the absorbance of P–NO-Hb decreased more slowly over time than those of Hb and NO-Hb. The results confirm that the presence of phosphate groups can increase the stability of Hb through structural changes.