Abstract
Cholinesterase (ChE) hydrolyzing acetylcholine (ACh) in vivo can be classified into two groups. The ChE localizing in brain and erythrocytes is known as ChE and hydrolyzes ACh and acetyl-β-methylcholine (MeCh) but not benzoylcholine (BzCh). The ChE localizing in liver and serum is termed pseudo ChE and hydrolyzes ACh and BzCh but not MeCh. Effects of BzCh, a specific substrate of pseudo ChE on true ChE in brain mitochondria and erythrocytes of rabbit and rat were studied. The ChE activities in rabbit brain with ACh and MeCh as substrates were decreased to 1/4 and 1/3 of the control activities by addition of 10 mM BzCh, respectively. The pS curve for ChE in rabbit brain and erythrocytes with ACh and MeCh as substrates markedly decreased by addition of 3 mM of BzCh. The inhibitory effect of BzCh was reversible and competitive, as assessed by a Lineweaver-Burk plot method. BzCh protected the irreversible inactivating effect of true ChE by DEP. These results suggest that BzCh is not hydrolyzed by true ChE but does have an affinity for the active center of true ChE.
