Partial-purification and Characterization of Angiotensin Converting Enzyme Inhibitory Proteins from the Leaves and Seeds of Moringa oleifera

Aim: To partially-purify, characterize and investigate the inhibition pattern of proteins from the leaves and seeds of Moringa oleifera.

Methodology: Crude proteins obtained from the leaves and seeds were partially-purified by a two-step method: cold acetone precipitation and sephadex G-75 gel filtration chromatography and Angiotensin Converting Enzyme (ACE) inhibitory activities determined using Cushman and Cheung method with some modifications on the assay conditions. The effects of pH, temperature and some digestive enzymes on the inhibitory proteins were determined. The inhibition pattern was also investigated using Lineweaver-Burk plots.

Results: The ACE inhibitory proteins from the leaves and seeds were purified 8.41 and 12.40 folds with a yield of 38 and 35.18%, respectively on sephadex G-75 column. The optimum pH and temperature of the inhibitory proteins were 8.2 and 37.6°C, for leaves and 7.8 and 39°C, for seeds, respectively. The partially-purified ACE inhibitors exhibited a mixed type of inhibition. The Km of inhibitory proteins obtained from the leaves increased from 3.51mM without the inhibitor to 4.79mM and 5.62mM in the presence of 0.5 and 1mg/ml of the inhibitor, respectively, while Vmax decreased from 0.953µmol/min without inhibitor to 0.784µmol/min and 0.629µmol/min, in the presence of 0.5 and 1mg/ml of the inhibitor, respectively, with a Ki of 3.51mM. For the seeds, the Km increased from 2.89mM (without inhibitor) to 5.747mM (at 1mg/ml inhibitor), while Vmax decreased from 0.910 (without inhibitor) to 0.628µmol/min (at 1mg/ml inhibitor), with a Ki of 1.58mg/ml. The digestive enzymes, pepsin and trypsin significantly (P<0.05) reduced the activity of the partially-purified inhibitors from both leaves and seeds compared to captopril. In conclusion, ACE inhibitory proteins from M. oleifera may be beneficial as nutraceutical or drug for blood pressure regulation in hypertensive patients.