Characterisation of partially purified milk-clotting enzyme from Solanum dubium Fresen seeds

The seeds of Solanum dubium were blended and extracted using different types of buffers. The most reliable, quick, and efficient buffer was found to be 5% NaCl in acetate buffer (pH 5.0) which was used throughout the study. The extract was filtered and fractionated twice with ammonium sulphate. The partially purified enzyme was characterised by SDS–PAGE which showed a band of molecular weight of 66 kDa with the presence of other bands of low density. When compared with other plant enzymes, S. dubium enzyme was found to have higher clotting and proteolytic activities. The activity of the enzyme was steadily increased with enzyme and substrate concentration. The enzyme was found to be very stable against a wide range of pH values as well as a wide range of temperature (20–90 °C). The results of substrate specificity of the enzyme showed that the partially purified enzyme preferred both hydrophilic and hydrophobic amino acid residues at P1 position. The catalytic efficiency of the purified enzyme was enhanced by an aliphatic amino acids (Leu) compared to aromatic residue (Phe) at P1 position at the same site.