The Effect of Tyrosyl Modification on the Activity of α-Lactalbumin in the Lactose Synthetase Reaction

The effect of nitration with tetranitromethane, iodination, and treatment with tyrosinase on the ability of bovine α-lactalbumin to act as a modifier in the lactose synthetase reaction was determined. Nitration modified tyrosine and tryptophan but not histidine, iodination modified tyrosine, tryptophan, and histidine, and tyrosinase modified tryptophan but not tyrosine. The loss of activity of α-lactalbumin in the lactose synthetase reaction was correlated closely with the loss of tyrosine in all cases. Inactive dimers and polymers of α-lactalbumin were formed during nitration and iodination.