The inhibitory effect of the neuromuscular blocking agent, gallamine triethiodide, on camel retina acetylcholinesterase activity

The present investigation addresses the mode of inhibition of the camel retinal acetylcholinesterase (AChE) activity by gallamine triethiodide, which is known to be a specific non-depolarizing neuromuscular blocking agent and polar cholinergic antagonist. This study gave the following results: it was found that gallamine (GA) reversibly inhibited the AChE activity in a concentration dependent manner, the IC50 being about 0.633 mM. The K-m for the hydrolysis of acetylthiocholine iodide by AChE was found to be 0.0803 mM in the control system, and the value increased by 19-463% in the GA (0.125-1.0 mM) treated systems. The V-max was 0.649 mu mol/min per mg protein for the control as well as GA treated systems. Dixon as well as Lineweaver-Burk plots and their secondary replots indicated that the nature of the inhibition is of the reversible competitive type. The K-i value was estimated as 0.160 mM. The K-i value increased with an increase in substrate concentration. The turnover number (K-cat) and specificity constant (K-sp) were 62.1 min(-1) and 7.73 x 10(5) (M . min)(-1) in the control system while the value for one parameter (K-sp) was decreased by 25-83% in the GA (0.125-1.0 mM) treated systems. Copyright (C) 1997 Elsevier Science Ireland Ltd.