CHARACTERIZATION OF ISOLECTINS IN TETRACARPIDIUM-CONOPHORUM SEEDS (NIGERIAN WALNUT)

A lectin preparation obtained from Tetracarpidium conophorum (Nigerian walnut) by affinity chromatography of seed extracts on lactose-agaros e has been shown to contain two components by gel filtration on Sephad ex G150. The larger component Tetracarpidium conophorum agglutinin I ( TCAI) is a disulphide-bonded 70 kDa homodimer whereas the second compo nent TCAII is a 34 kDa monomeric protein. Amino terminal aminoacid seq uencing shows identity in TCAI and TCAII for the first fifteen residue s after which the sequences diverge. The N-terminal sequences of TCAI and TCAII show identity with sequences in the B-chains of ricin and Ri cinus communis agglutinin I (RCAI) in eleven of the initial fifteen re sidues. Thereafter TCAI appears to be homologous to the ricin B chain whereas TCAII is more homologous with the B chain of RCAI. A limited s creening of the carbohydrate-binding specificity of TCAII by affinity chromatography of defined oligosaccharides on TCAII Sepharose columns shows that the binding specificity reported earlier for affinity purif ied Tetracarpidium conophorum isolectins (Sato S, Animashaun T, Hughes RC (1991) J Biol Chem 266:11485-94) reflects the binding properties o f TCAII which is the major isolectin in unfractionated lectin preparat ions.