Partial properties of an aspartic protease in bitter gourd (Momordica charantia L.) fruit and its activation by heating

Bitter gourd (BG fruit) is usually heated in hot water to reduce bitterness and improve flavour before being served. Protein extract from BG was analyzed for protease activity by gelatin-gel electrophoresis. The study showed that the proteolytic activity in BG flesh was enhanced by heat-treatment at temperatures ranging from 50 °C to 75 °C. An aspartic protease (AP) was characterized by gel electrophoresis. The optimal AP activity was at pH 7; the pI of the AP was demonstrated to be 4.8; the protein molecular weight of the BG–AP was estimated to be 60 KD by SDS–PAGE. The AP was implicated in the proteolysis of the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase.The AP was further purified and submitted for analysis of peptide mass fingerprint (PMF). The Mascot peptide mass fingerprint of the AP protein hit no existing protein (score > 60), and it proved to be a novel AP.