Iris hybrid agglutinin (IRA) is isolated from dutch iris. IRA is a heterodimer that consists of two peptide chains, 27,000 and 34,000, linked by disulfide bonds. It has an isoelectric point between pH 7.2 and pH 7.4. This lectin agglutinates both native and trypsin-treated rabbit erythrocytes, not human erythrocytes, with specificity for blood group O and also agglutinates A and B erythrocytes.
IRA is N-acetylgalactosamine specific and elutes with sugar GalNAc?1-3Gal?-O. GalNAc ?1-3[L-Fuc ? 1-2]Gal and GalNAc ?1-3GalNAc are noninhibitory which suggests the importance of a free equatorial hydroxyl group at the C-2 position of the penultimate galactose for lectin binding. Either acetamido group or a fucosyl group at this position appears to cause steric hindrance, thus abolishing binding to the lectin.
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