Residue Gln-30 of human erythrocyte anion transporter is a prime site for reaction with intrinsic transglutaminase.

Elevating the intracellular concentration of Ca2+ ions in human erythrocytes leads to the formation of membrane-associated polymers, composed of skeletal and cytoplasmic proteins. The anion transporter band 3 serves as a membrane anchor for this N epsilon-(gamma-glutamyl)lysine cross-linked polymer. The reaction is catalyzed by an intrinsic transglutaminase, and it can be observed in broken cells merely by the addition of Ca2+. Certain primary amines, such as dansylcadaverine, inhibit the process by virtue of competition against the epsilon-lysyl or donor functionalities of the protein substrates. Dansylcadaverine itself becomes incorporated into the enzyme-specific gamma-glutaminyl or acceptor residues, blocking these from participating in the formation of protein-to-protein cross-links. This labeling procedure, coupled with an anti-dansyl antibody affinity procedure to isolate dansyl-labeled compounds, was employed to identify Gln-30 as the preferred transglutaminase-reactive acceptor site in the band 3 protein.