The effect of calcium on bovine α-lactalbumin conformational transitions by ultraviolet difference and fluorescence spectrophotometry

RK Owusu

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

The unfolding of bovine α-lactalbumin (BAL) in guanidine hydrochloride (GnHCl) was studied by UV difference and fluorescence spectrophotometry. When BAL was dissolved in calcium-free solvents, nonsuperimposable unfolding profiles were observed. Thus, it may be concluded that the two spectrophotometric techniques are sensitive to different BAL chromophores or levels of structural organisation.In a solvent containing calcium (0·1 m Tris-HCl buffer, pH 7·0; 9 mm calcium chloride) there was an increase in the molar UV difference absorbance change associated with GnHCl unfolding of BAL. Unfolding profiles were also biphasic, i.e. denaturation occurred in two stages at different GnHCl concentrations. This pattern of unfolding is different from the usual S-shaped profiles recorded for the three- or two-state BAL unfolding reaction. The results suggest that BAL possesses a more compact structure in the presence of calcium ions. The biphasic transition may arise from the loss of structure, which is unique to calcium-stabilised BAL.
Original languageEnglish
Pages (from-to)41-45
JournalFood Chemistry
Volume43
Issue number1
DOIs
Publication statusPublished - 1992

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fluorescence emission spectroscopy
Ultraviolet Spectrophotometry
Lactalbumin
lactalbumin
Fluorescence Spectrometry
Spectrophotometry
Fluorescence
Calcium
calcium
cattle
guanidines
Guanidine
Calcium Chloride
Tromethamine
Denaturation
Chromophores
denaturation
calcium chloride
absorbance
Buffers

Cite this

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title = "The effect of calcium on bovine α-lactalbumin conformational transitions by ultraviolet difference and fluorescence spectrophotometry",
abstract = "The unfolding of bovine α-lactalbumin (BAL) in guanidine hydrochloride (GnHCl) was studied by UV difference and fluorescence spectrophotometry. When BAL was dissolved in calcium-free solvents, nonsuperimposable unfolding profiles were observed. Thus, it may be concluded that the two spectrophotometric techniques are sensitive to different BAL chromophores or levels of structural organisation.In a solvent containing calcium (0·1 m Tris-HCl buffer, pH 7·0; 9 mm calcium chloride) there was an increase in the molar UV difference absorbance change associated with GnHCl unfolding of BAL. Unfolding profiles were also biphasic, i.e. denaturation occurred in two stages at different GnHCl concentrations. This pattern of unfolding is different from the usual S-shaped profiles recorded for the three- or two-state BAL unfolding reaction. The results suggest that BAL possesses a more compact structure in the presence of calcium ions. The biphasic transition may arise from the loss of structure, which is unique to calcium-stabilised BAL.",
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The effect of calcium on bovine α-lactalbumin conformational transitions by ultraviolet difference and fluorescence spectrophotometry. / Owusu, RK.

In: Food Chemistry, Vol. 43, No. 1, 1992, p. 41-45.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The effect of calcium on bovine α-lactalbumin conformational transitions by ultraviolet difference and fluorescence spectrophotometry

AU - Owusu, RK

PY - 1992

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N2 - The unfolding of bovine α-lactalbumin (BAL) in guanidine hydrochloride (GnHCl) was studied by UV difference and fluorescence spectrophotometry. When BAL was dissolved in calcium-free solvents, nonsuperimposable unfolding profiles were observed. Thus, it may be concluded that the two spectrophotometric techniques are sensitive to different BAL chromophores or levels of structural organisation.In a solvent containing calcium (0·1 m Tris-HCl buffer, pH 7·0; 9 mm calcium chloride) there was an increase in the molar UV difference absorbance change associated with GnHCl unfolding of BAL. Unfolding profiles were also biphasic, i.e. denaturation occurred in two stages at different GnHCl concentrations. This pattern of unfolding is different from the usual S-shaped profiles recorded for the three- or two-state BAL unfolding reaction. The results suggest that BAL possesses a more compact structure in the presence of calcium ions. The biphasic transition may arise from the loss of structure, which is unique to calcium-stabilised BAL.

AB - The unfolding of bovine α-lactalbumin (BAL) in guanidine hydrochloride (GnHCl) was studied by UV difference and fluorescence spectrophotometry. When BAL was dissolved in calcium-free solvents, nonsuperimposable unfolding profiles were observed. Thus, it may be concluded that the two spectrophotometric techniques are sensitive to different BAL chromophores or levels of structural organisation.In a solvent containing calcium (0·1 m Tris-HCl buffer, pH 7·0; 9 mm calcium chloride) there was an increase in the molar UV difference absorbance change associated with GnHCl unfolding of BAL. Unfolding profiles were also biphasic, i.e. denaturation occurred in two stages at different GnHCl concentrations. This pattern of unfolding is different from the usual S-shaped profiles recorded for the three- or two-state BAL unfolding reaction. The results suggest that BAL possesses a more compact structure in the presence of calcium ions. The biphasic transition may arise from the loss of structure, which is unique to calcium-stabilised BAL.

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