Kinetics of Acetylcholinesterase Inhibition of Quisqualis indica Linn. Flower Extract

Rangoon creeper (Quisqualis indica Linn.) is a plant of the family Combretaceae. In Thai traditional medicine, its seeds contain oil and quisqualic acid that act as anthelminthic. Its flowers are used against diarrhea and eaten as vegetable. The flower extract gave high total polyphenol contents and showed strong antioxidant activity. In the search for new acetylcholinesterase inhibitors from plant origin, it was demonstrated that methanolic extract of Q. indica flower exhibited this activity. The extract inhibited electric eel acetylcholinesterase in dose dependent manner with an IC50 value of 0.77 μg/ml. The Michaelis-Menten constant (Km) for the hydrolysis of acetylthiocholine iodide was 0.034 mM. The Km value in the presence of the extracts (Kmapp) at first decreased, and then increased by 60-88.9%. The Vmax was 0.017 μM/min/μg protein. The Vmax value in the presence of the extracts (Vmaxapp) decreased by 2.8-52.3%. The estimated value of KI was 1.41 mM, respectively. The Lineweaver-Burk plot, Dixon plot and their replots showed combination of the mixed and partially noncompetitive inhibition.