Properties of sulfanilazo-haptoglobin

1. Tyrosine and two structural isomers of histidine residues in human haptoglobin were modified with diazotized sulfanilic acid. Sulfanilazo-derivatives of haptoglobin obtained by increasing the reagent/protein molar ration showed gradual decrease of peroxidase activity when complexed with hemoglobin. 2. Formation of haptoglobin derivatives with ten mono(sulfanilazo)-tyrosines and two mono (sulfanilazo)histidines resulted in the blockage of one out of six antigenic determinants, whereas immunoreactivity of the derivative with fourteen azotyrosines, one C-4, and two C-2 azohistidines was decreased by half. 3. Removal of sialic acid from oligosaccharide chains of haptoglobin made the molecule more accessible to diazotized sulfanilic acid. 4. Sulfanilazo-modification of tyrosine and histidine residues was practically of no effect in the reaction of haptoglobin with plant lectin, concanavalin A.