ABSTRACT
BACKGROUND: By resisting digestion in the stomach, the major bovine milk allergen, beta-lactoglobulin, is believed to act as a transporter of vitamin A and retinol to the intestines. beta-Lactoglobulin has 2 intramolecular disulfide bonds that may be responsible for its allergic effects. OBJECTIVE: This study was carried out to assess the importance of disulfide bonds to the allergenicity and digestibility of beta-lactoglobulin. METHODS: beta-Lactoglobulin was subjected to reduction by the ubiquitous protein thioredoxin, which was itself reduced by the reduced form of nicotinamide adenine dinucleotide phosphate by means of nicotinamide adenine dinucleotide phosphate-thioredoxin reductase. Digestibility was measured with a simulated gastric fluid; results were analyzed by SDS-PAGE. Allergenicity was assessed with an inbred colony of high IgE-producing dogs sensitized to milk. RESULTS: As found for other proteins with intramolecular disulfide bonds, beta-lactoglobulin was reduced specifically by the thioredoxin system. After reduction of one or both of its disulfide bonds, beta-lactoglobulin became strikingly sensitive to pepsin and lost allergenicity as determined by skin test responses and gastrointestinal symptoms in the dog model. CONCLUSION: The results provide new evidence that thioredoxin can be applied to enhance digestibility and lower allergenicity of food proteins.
