Chickpea pa2 albumin binds hemin

The pa2 albumin in chickpea seeds is a lectin that causes red blood cell agglutination. The sequence of the homologue pa2 albumin in peas contains four hemopexin like domains. Since hemopexin binds hemin with great affinity, the possibility that chickpea pa2 also binds hemin has been investigated. Spectrophotometric studies showed that the interaction of pa2 with hemin results in an increase in absorbance at 401 nm (Soret region). This increase is proportional to the concentration of hemin and pa2 in a saturable manner. Scatchard and non-linear regression analyses revealed that 1.2 molecules of hemin bind to 1 pa2 molecule. Native electrophoresis followed by staining to reveal peroxidase activity confirmed hemin binding. The significance of hemin binding by pa2 is discussed in relation to the spatial and temporal localization of pa2 in plants. Binding of hemin by pa2 highlights the fact that at least some lectins can bind a variety of small hydrophobic ligands as well as carbohydrates.