Purification, Characterization and Functional Analysis of a Serine Protease Inhibitor from the Pulps of Cicer arietinum L. (Chick Pea)

Abstract

Serine proteinase inhibitors (SPIs) are present in high amount in legume seeds where they play an important role in plant defence mechanism against pests. In the present study, a serine protease inhibitor has been identified from the seeds of Cicer arietinum (L.) and characterized for its inhibitory potency against trypsin and chymotrypsin. Ammonium sulphate fractionation was executed as an initial step to purify the inhibitor. The fraction which was obtained from 30-60% relative ammonium sulphate saturation exhibited the maximum trypsin inhibition activity against 0.2% casein using radial diffusion method. The 30–60% fraction was further subjected to ion exchange chromatography using 1 mL HiTrap Q HP column. The peak fractions were analyzed for the enzymatic activity and also characterized on 12% SDS PAGE. The results indicated that the flow through fraction has retained a significant proteolytic inhibition towards trypsin with a relative molecular mass of approximately 12-13 kDa. The kinetic results have demonstrated that the purified inhibitor from Cicer arietinum L. not only inhibited trypsin but also chymotrypsin. The Circular Dichroism spectrum analysis of the purified inhibitor has revealed that the secondary structure content is highly composed of random coils which were supported by the reports of other low molecular weight trypsin inhibitors. To conclude, a low molecular weight serine protease inhibitor possessing both trypsin and chymotrypsin inhibition from the seeds of C. arietinum has been purified, characterized and the results are reported.