Changes in trout hemoglobin conformations and solubility after exposure to acid and alkali pH |
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| Authors: | Kristinsson Hordur G Hultin Herbert O |
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| Institution: | Department of Food Science and Human Nutrition, University of Florida, Gainesville, Florida 32611, USA. hgkristinsson@mail.ifas.ufl.edu |
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| Abstract: | The effect of different acid and alkali treatments followed by pH readjustment on solubility and conformation of trout hemoglobins was investigated. At low pH (1.5-3.5) hemoglobin was unfolded at faster rates as the pH was lowered. Inclusion of 500 mM NaCl at low pH significantly increased the rate of unfolding. At alkaline pH (10-12) the conformation of hemoglobin was much less affected than at acid pH, and the presence of salt had little additional effect. When hemoglobin solutions were adjusted to neutrality at different stages of unfolding, the recovery of native structure on refolding was proportional to the extent of unfolding prior to pH readjustment: the more unfolded the protein, the less was the recovery of native structure. The presence of salt led to a smaller recovery of native structure. The more improperly unfolded the hemoglobin was (and hydrophobic), the lower was its solubility. Results suggest that the presence of NaCl (25-500 mM) may not only interfere with the refolding process but also enhance the hydrophobic interactions of improperly refolded hemoglobin, possibly due to charge screening. These results show that proper control of unfolding and refolding time and ionic strength in processes using highly acidic or alkaline conditions can minimize loss of hemoglobin solubility. |
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