Sulfhydryl group activation for commercial β-lactoglobulin measured using κ-casein 2-thio, 5′nitrobenzoic acid

The process of activation converts protein sulfhydryl (SH) groups from the masked state to a free state with increased reactivity. Beta-lactoglobulin (beta-Lg) SH group activation was measured, in phosphate buffer (pH 6.8) using K-casein 2-thio, 5'-nitrobenzoic acid (Cn-Ellman), at 412 nm. Reaction transition state parameters from 25-55degreesC and 60-80degreesC were not significantly different. Present results were compared with differential scanning calorimetry (DSC) traces for beta-Lg heat unfolding, temperature-reaction profiles for whey or beta-Lg heat aggregation, and also SH-activation in skim milk. The findings reveal that SH-group activation precedes heat unfolding and aggregation of beta-Lg. Further studies using protein disulfide reagents such. as Cn-Ellman will help to elucidate the mechanism of SH group activation for beta-Lg. (C) 2003 Published by Elsevier Ltd.