Preliminary study on the isolation and partial characterization of low molecular weight proteins in selected legumes

The isolation of low molecular weight (LMW) proteins in selected legumes revealed the presence of LMW proteins ranging from 10,500 to 22,000 in malunggay seed (Moringa oleifera L.) and velvet bean (Mucuna pruriens). LMW proteins were also present in jack bean (Canavalia ensiformis) and sword bean (Canavalia gladiata) but were minor components. Isolated LMW proteins (peak 3) by gel filtration in Sephadex G-75 column had an estimated molecular weight of 10,500 in malunggay seed. A group of LMW proteins in peak 2 (12,500, 14,500, 20,000 and 24,000) was present in velvet bean as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. LMW proteins (13,500-18,000) were present as minor components in jack bean and sword bean but were not isolated for further investigation. High levels of glutamic acid (9.39-21.23%), glycine (11.59-14.04%), aspartic acid (5.5-15.24%) and arginine (5.30-14.14%) were observed in the isolated fractions. These LMW proteins were nutritionally high in cysteine (malunggay LMW protein), threonine, valine, leucine, isoleucine, and tryptophan. However, they were found deficient in lysine (malunggay LMW protein) and sulfur-containing amino acid (velvet bean LMW protein). LMW proteins exhibited high thermal stability up to 100 deg C. Digestibility assay revealed high proteolytic activity by trypsin, chymotrypsin and aminopeptidase in heated condition and lesser degree in its native form. Antitryptic activity was lower in LMW proteins than the corresponding total protein of velvet bean and malunggay seeds. Strong hemagglutinating activity was observed for the total protein of malunggay seed against types O and B of human RBC however was not detectable in the LMW protein as well as on the total protein of velvet bean. Qualitatively, enzyme-linked immunosorbent assay (ELISA) showed moderate antigenic activity in malunggay seed total protein and weak activity for the isolated LMW protein. Velvet bean total protein showed a weak immunoactivity while none was observed in LMW protein.