Choline acetylthio

The most outstanding example illustrating this strategy came from the team of Alain Friboulet and Daniel Thomas, who produced anti-idiotype antibodies against a monoclonal antibody AE2 that was a competitive inhibitor of acetylcholine esterase. One of the selected antibodies, 9A8, catalyzes the hydrolysis of acetylthio-choline with a pseudo first-order rate constant /feat = 81 and a factor of acceleration of 4.2 x 10 . These remarkable parameters, which are only two orders of magnitude lower when compared to those of the enzyme, make abzyme 9A8 the most powerful abzyme known until now. 

Quantification of Cholinesterase Activity in Serum Adjustthe temperature of 3 ml of dithiobisnitrobenz-oic acid solution to 25°, add 20 ll1 of the serum sample and 0.1 ml of a 5% solution of acetylthio-choline iodide, mix well, and record the absorbance of a 1-cm layer at 405 nm at 30-second intervals over a period of 2 minutes. If the change in absorbance exceeds 0.2 in 30 seconds, dilute the sample 1 in 10 with normal saline and repeat the measurements (the readings must then be multiplied by 10). The concentration of cholinesterase is calculated as follows ... 

Acetylcholinesterase is mechanistically related to serine proteases and involves acylation of Ser and contains the catalytic triad Ser -His -Glu. Precise data for acetylation by the natural substrate acetylcholine is difficult to obtain due to lack of a convenient assay method, so the mechanistically equivalent surrogate acetylthio-choline has frequently been used to probe mechanistic aspects of this enzyme [15]. To explore proton transfer reactions that accompany acetylation by this substrate, solvent isotope effect measurements and proton inventories on k /Km have been conducted [16, 17]. The isotope effects are near unity and the proton inventories bowed-upwards, suggesting that the transition state for kjKm is a virtual transi-... 

In 1990, we reported [ 166] that CPT-11 inhibits acetylcholinesterase activity. In the paper, the rate of thiocholine (TCh) production from acetylthio-choline iodide (ATChl) by acetylcholinesterase was analyzed with Line-weaver-Burk plots (Figure 2.3). This kinetic analysis indicated that CPT-11 noncompetitively inhibited acetylcholinesterase. In this case, the apparent Michaelis constant (Km) and inhibition constant (Ki) ranged from 63 to 68 yUM and from 0.221 to 0.300 /iM, respectively (Table 2.3). The same analysis revealed that the Ki value of physostigmine (a potent acetylcholinesterase... 

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