Purification of peanut (Arachis hypogaea) agglutinin isolectins by chromatofocusing

This report describes the purification and isolation of the isolectins of peanut agglutinin (PNA). We find the affinity-purified PNA to have an amino acid composition similar to that reported by Lotan et al. (J. Biol. Chem. 250, 8518-8523 (1975)); however, our preparation contains three tryptophan residues per subunit rather than two as reported by Lotan et al. This higher tryptophan content is consistent with the extinction coefficient (E1 mg/ml 280) of 0.96 as previously reported (Fish et al., Arch. Biochem. Biophys. 190, 693-698 (1978)). The PNA, purified by affinity chromatography on lactosyl-Sepharose, contains six major and three minor components capable of agglutinating neuraminidase-treated erythrocytes. Seven of the isolectins were obtained in a highly purified form by chromatofocusing, a column chromatographic technique which separates proteins on the basis of their isoelectric points. Isoelectric focusing of the purified isolectins indicates that they have the following isoelectric points: A, 6.70; B, 6.55; C, 6.35; D, 6.25; E, 6.10; F, 5.90; and G, 5.70. Preliminary studies on the subunit composition of the isolectins are also presented.