To obtain information about the evolution of the cholinesterases, acetylcholines‐terase (AChE) and butyrylcholinesterase (BuChE) in the vertebrates, we investigated the cholinesterase (ChE) activity of the cephalochordate amphioxus (Branchiostoma floridae and Branchiostoma lanceolatum). On the basis of evidence from enzymology, pharmacology, and molecular biology, we conclude that amphioxus possesses two ChE activities and two ChE genes. Two covalent inhibitors of cholinesterases were able to pharmacologically isolate the two activities as drug‐sensitive ChE and drug‐resistant ChE. Kinetically, in terms of substrate specificity, the drug‐sensitive ChE resembles vertebrate AChE, and the drug‐resistant ChE resembles the BuChE of cartilaginous and bony fish or the intermediate ChE of protostome invertebrates. We also used the polymerase chain reaction with degenerate oligonucleotide primers and genomic DNA to obtain clones of 1,574 and 1,011 bp corresponding to two cholinesterase genes from amphioxus, which we designated as ChE1 and ChE2. ChE2 codes for an enzyme with an acyl‐binding pocket sequence, a portion of the protein that plays an important role in determining substrate specificity, typical of invertebrate ChE. ChE1, which contains a 503‐bp intron, encodes a protein with a novel acyl binding site. Phylogenetic analysis of the sequences suggests that the two genes are a result of a duplication event in the lineage leading to amphioxus. We discuss the relevance of our results to the evolution of the cholinesterases in the chordates. Previously, we reported that amphioxus contained a single cholinesterase activity with properties intermediate to AChE and BuChE (Pezzementi et al. [1991] In: Cholinesterases: Structure, Function, Mechanism, Genetics and Cell Biology. J. Massoulié et al., eds. ACS: Washington, D.C., pp. 24–31). J. Exp. Zool. 277:213–229, 1997. © 1997 Wiley‐Liss, Inc.
25%, 50% and 75% ( 2.32 • 1.41, 3.90 • 1.85 and 6.88 • 2.66 rain) was accelerated compared with control (3.36 • 1.34, 5.78 • 2.22, and 8.58 • 3.60, and), but recovery to 95% (18.53 • 9.09 vs 13.29 • 5.24 min) was delayed. Also, TR recovery to 50%, 70%, and 90% was slower (14.47 • 8.73, 21.25 • 11.06 Supported by an education grant from Burroughs Wellcome Co. June, 1996. 31.37 • 12.11 min vs 11.75 • 3.74, 13.78 • 4.39 and 17.86 • 6.44 rain ). However, all T 1 and TR recovery times were decreased in the edrophonium group (0.88 • 0.51, 2.00 • 1.50, 4.97 • 2.96, and 9.35 • 5.24 rain for Tt and 6.86 • 3.93, 9.05 +_ 4.51 and 12.24 • 6.66 Accepted for publication 19th
In obstetric patients undergoing postpartum tubal ligation, we found that metoclopramide produced dose-dependent prolongation of suxamethonium-induced neuromuscular block. Mean block times after suxamethonium 1 mg kg-1 were 8.0 min, 9.83 min and 12.45 min for control and metoclopramide 10 mg and metoclopramide 20 mg groups, respectively. A laboratory study was therefore conducted on the inhibition of human plasma cholinesterase (PCHE) and erythrocyte acetylcholinesterase (ACHE) activity by varying concentrations of metoclopramide using acetylthiocholine as substrate. PCHE showed a greater sensitivity to inhibition by metoclopramide; the concentration of metoclopramide producing 50% inhibition of activity (I50) was 3.16 x 10(-7) mol litre-1, which is within the therapeutic range. ACHE was less sensitive to inhibition by metoclopramide (I50 2.24 x 10(-5) mol litre-1). Analysis of enzyme kinetics at varying substrate concentrations revealed that metoclopramide produced a potent non-competitive, dose-dependent inhibition of both ACHE and PCHE. The inhibition constant, Ki, was 1.88 x 10(-7) mol litre-1 for PCHE and 9.5 x 10(-8) mol litre-1 for ACHE. As metoclopramide is a potent inhibitor of PCHE, interactions might be expected to occur between metoclopramide and drugs that require PCHE for biotransformation, such as suxamethonium and ester local anaesthetics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.