A new serine protease from the leaves of Thespesia populnea

A serine protease was purified 6.9-fold from the leaves of Thespesia populnea using ammonium sulfate fractionation followed by CM-cellulose and Sephadex G-100 chromatography. The purified enzyme was named populnein and was characterized. It was made up of a single polypeptide, and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) analysis showed that the enzyme had a molecular mass of 14,518 Da. Inhibition of enzyme activity by phenyl methane sulfonyl fluoride indicates that populnein belongs to the class of serine proteases. The enzyme had appreciable pH and temperature stability. The activity of the enzyme was optimal at pH 8.0 and temperature 40°C. The enzyme was thermostable and retained 85% of its activity at 70°C after 1 hr. The enzyme was also resistant to autodigestion. The stabilization of the membrane of red blood cells exhibited by the protease populnein was found to be higher than for diclofenac. More studies are necessary to investigate the biological activity and applications of serine protease of T. populnea.