Separation and some properties of Aloe vera L. leaf pulp lectins

The separation and partial purification of two lectins from the leaf pulp of Aloe vera L. (=barbadensis Miller) is presented. The fraction showing haemagglutinating activity was precipitated at 50% ammonium sulphate concentration from the crude leaf pulp extract. The precipitate thus obtained, after dialysis, was applied to a hydroxylapatite column. Stepwise elution resulted in two peaks showing haemagglutinating activity eluted with 5 mM (Aloctin I) and 20 mM (Aloctin II) phosphate buffers. Haemagglutinating activity was estimated visually by adding a 4% rabbit erythrocyte suspension to serial two-fold dilutions of the lectins in microtitration plates. None of the 20 sugars tested inhibited haemag--glutinating activity of Aloctin I up a concentration of 500 mM. Aloctin II was inhibited by N-acetyl-D--galactosamine at 250 mM concentration. Of 10 metal ions tested, only Al(3+) salts were found to activate Aloctin I and II. On the other hand, it was shown that neither lectin possessed any alpha- and beta- galactosidase or alpha- and beta- glucosidase activity. The lectins were of glycoprotein structure containing approximately 5% neutral sugar. The specificity of the lectins towards human and rat erythrocytes was investigated.