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Stable monomeric intermediate with exposed Cys-119 is formed during heat denaturation of β-lactoglobulin

2003; Elsevier BV; Volume: 301; Issue: 2 Linguagem: Inglês

10.1016/s0006-291x(02)02997-2

1090-2104

Thomas Croguennec, Saı̈d Bouhallab, Daniel Mollé, Brendan T. O’Kennedy, Raj Mehra,

Enzyme Production and Characterization

The role of the free sulfhydryl group of β-lactoglobulin in the formation of a stable non-native monomer during heat-treatment of β-lactoglobulin solutions was investigated. Two concomitant events occurred at the earlier stage of heating: unfolding of native globular monomer and intramolecular sulfhydryl/disulfide exchange reaction. Thus, two denatured monomeric species were formed: a non-native monomer with exposed Cys-121 (Mcys121) which became reversible after cooling, and a stable non-native monomer with exposed Cys-119 (Mcys119) which exhibited both a larger hydrodynamic conformation than native monomer and low solubility at pH 4.7. The results also show that the formation of these monomeric species throughout heat-induced denaturation of native β-lg monomers is faster than their subsequent aggregation. A mechanism describing the behavior of β-lg denaturation/aggregation during heat-treatment under selected conditions (5.8 mg/ml, low ionic strength, pH 6.6, 85 °C) is presented.