• BMB Reports
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• v.36 no.2
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• pp.149-153
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• 2003

The dibucaine number (DN) was determined for serum cholinesterase (EC 3.1.1.8, SChE) in plasma samples. The ones with a DN of 79-82 were used, because they had the "usual" SChE variant. The enzyme was assayed colorimetrically by the reaction of 5,5'-dithiobis-[2-nitrobenzoic acid] (DTNB) with the free sulfhydryl groups of thiocholine that were produced by the enzyme reaction with butrylthiocholine (BuTch) or acetylthiocholine (AcTch) substrates, and measured at 412 nm. Dibucaine, a quaternary ammonium compound, inhibited SChE to a minimum within 2 min in a reversible manner. The inhibition was very potent. It had an $IC_{50}$ of $5.3\;{\mu}M$ with BuTch or $3.8\;{\mu}M$ with AcTch. The inhibition was competitive with respect to BuTch with a $K_i$ of $1.3\;{\mu}M$ and a linear-mixed type (competitive/noncompetitive) with respect to AcTch with inhibition constants, $K_i$ and $K_I$ of 0.66 and $2.5\;{\mu}M$, respectively. Dibucaine possesses a butoxy side chain that is similar to the butryl group of BuTch and longer by an ethylene group from AcTch. This may account for the difference in inhibition behavior. It may also suggest the existence of an additional binding site, other than the anionic binding site, and of a hydrophobic nature.

• Applied Microscopy
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• v.18 no.2
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• pp.34-46
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• 1988

The stimulation-secretion coupling in the pancreatic acinar cell have been studied by electron microscope. Morphological changes in the cells exhibited the cellular response induced by acetylcholine and MNNG. MNNG, a guanylate cyclase activator, induced the formation of numerous secretory granules in a period after the agent administration. This result suggest that guanylate cyclase potentiated the early sustained response in pancreatic acinar cells stimulated by acetylcholine. Cycloheximide and dibucaine reduced the secretory granules in number during sustained period. In pancreatic acinar cells, the secretion granules were considered to be directly packaged from cisternal space of endoplasmic reticulum.