title: Acid-induced unfolding of flounder hemoglobin: evidence for a molten globular state with enhanced pro-oxidative activity.
abstract: The acid-induced unfolding of flounder oxyhemoglobin was investigated and the effect on pro-oxidative activity assessed. Hemoglobin exhibited multistep unfolding transitions as pH was lowered, with the major transition between pH 3.5 and 4 5. The protein was maximally acid-unfolded (but not fully unfolded) at approximately pH 2.5, and further titration with HCl led to a partially refolded protein due to a stabilizing effect of Cl(-) anions. At low pH, the protein retained a sizable amount of secondary structure and had increased ANS binding, suggesting a molten globular form at low pH. Dramatic changes in the heme environment occurred concurrently with the changes in protein conformation. These changes resulted in an enhancement in the pro-oxidative activity of the protein. The results show that an increase in flounder hemoglobin pro-oxidation was correlated with the extent of its unfolding, and they provide useful insight into what may occur with hemoglobin in processes where highly acidic conditions are employed.
authors.affiliation: Laboratory of Aquatic Food Biomolecular Research, Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida 32611, USA. hgkristinsson@mail.ifas.ufl.edu
authors.forename: Hordur G
authors.initials: HG
authors.lastname: Kristinsson
mesh_terms: D000818:Animals; D001665:Binding Sites; D005432:Flounder / Q000097:blood*; D006454:Hemoglobins / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D019787:Linoleic Acid / Q000737:chemistry; D015227:Lipid Peroxidation; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood; D011487:Protein Conformation; D017510:Protein Folding; D013053:Spectrophotometry; D014364:Tryptophan / Q000737:chemistry
chemical_list: D006454:Hemoglobins; D016877:Oxidants; D006639:Histidine; D014364:Tryptophan; D019787:Linoleic Acid; D007501:Iron; D010100:Oxygen