Two lectins from the seeds of lablab bean (Lablab purpureus Linn cv. Highworth)

Two mitogenic lectins were isolated from the seeds of lablab bean (Lablab purpureus Linn cv. Highworth) by protein extraction using phosphate buffered saline (PBS) pH 7.2, ammonium sulfate fractionation and gel permeation chromatography using superfine Sephadex G-200. Both lectins were non-blood type specific but blood group specific because they agglutinated untreated blood types A, B, O and AB but not trypsinized and untrypsinized blood from calf and goat. Hemagglutination by lectin 1 was inhibited by the addition of D-fructose, D-glucose, maltose, sucrose and methyl-alpha-D-manno-pyranoside using blood type O and by D-glucose and D-mannose using blood type B. Lectin 2 was inhibited by D-fructose, D-mannose, D-glucose and methyl-alpha-D-mannopyranoside regardless of blood type. Among the haptenic sugars, strongest inhibition was elicited by methyl-alpha-D-mannopyranoside. Agglutination of blood types A and AB by lectin 1 was not inhibited by any of the sugars used. Precipitation of lectins 1 and 2 occurred at pH 4-5 and 8-9 respectively, indicating that their isoelectric point lie in these ranges and that the former is a basic protein while the latter is acidic. Activity of both lectins were stable from pH 2-12. Extreme temperature destroyed the activity of both lectins. Optimum temperature for lectin 1 activity was 40-50 deg C using blood types B and O, and 50 deg C for lectin 2 using blood type O. Using gel permeation chromatography, the molecular weights of lectins 1 and 2 were estimated to be 267 and 57 KD, respectively. From SDS-PAGE, lectin 1 was found to consist of six sub-units with apparent molecular weights of 32, 35.5, 39, 51.5, 55.5 and 59.5 KD. Lectin 2 was made up of sub-units with MW 15 and 17.5 KD, presumably of the alpha sub 2 beta, sub 2 type. Lectin 1 and 2 were found to be glycoproteins containing 2.30 percent and 4.23 percent total sugars, respectively. The reducing sugar residues were identified to be glucose and galactose by high performance liquid chromatography (HPLC). Both lectins contained high amounts of aspartate and glutamate, a large proportion of which exist in the amide form. Lectin 1 was also rich in lysine and histidine