Polymorphism of pseudocholinesterase in Torpedo marmorata tissues: comparative study of the catalytic and molecular properties of this enzyme with acetylcholinesterase.
We report the existence, in Torpedo marmorata tissues, of a cholinesterase species (sensitive to 10(-5) M eserine) that differs from acetylcholinesterase (AChE, EC 3.1.1.7) in several respects: (a) The enzyme hydrolyzes butyrylthiocholine (BuSCh) at about 30% of the rate at which it hydrolyzes acetylthiocholine (AcSCh), whereas Torpedo AChE does not show any activity on BuSCh. (b) It is not inhibited by 10(-5) M BW 284C51, but rapidly inactivated by 10(-8) M diisopropylfluorophosphonate. (c) It does not exhibit inhibition by excess substrate up to 5 X 10(-3) M AcSCh. (d) It does not cross-react with anti-AChE antibodies raised against purified Torpedo AChE. This enzyme is obviously homologous to the "nonspecific" or pseudocholinesterase (pseudo-ChE, EC 3.1.1.8) that exists in other species, although it is closer to "true" AChE than classic pseudo-ChE in several respects. Thus, it shows the highest Vmax with acetyl-, and not propionyl- or butyrylthiocholine, and it is not specifically sensitive to ethopropazine. Pseudo-ChE is apparently absent from the electric organs, but represents the only cholinesterase species in the heart ventricle. Pseudo-ChE and AChE coexist in the spinal cord and in blood plasma, where they contribute to AcSCh hydrolysis in comparable proportions. Pseudo-ChE exists in several molecular forms, including collagen-tailed forms, which can be considered as homologous to those of AChE. In the heart the major component of pseudo-ChE appears to be a soluble monomeric form (G1). This form is inactivated by Triton X-100 within days.(ABSTRACT TRUNCATED AT 250 WORDS)
Toutant
J P
JP
Massoulié
J
J
Bon
S
S
D000110:Acetylcholinesterase / Q000097:blood / Q000276:immunology / Q000378:metabolism*; D000818:Animals; D002091:Butyrylcholinesterase / Q000097:blood / Q000276:immunology / Q000378:metabolism*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D002802:Cholinesterases / Q000378:metabolism*; D004557:Electric Organ / Q000201:enzymology; D000939:Epitopes / Q000276:immunology; D009206:Myocardium / Q000201:enzymology; D011110:Polymorphism, Genetic; D012995:Solubility; D013116:Spinal Cord / Q000201:enzymology; D013379:Substrate Specificity; D014018:Tissue Distribution; D014101:Torpedo / Q000378:metabolism*
D002800:Cholinesterase Inhibitors; D000939:Epitopes; D000110:Acetylcholinesterase; D002091:Butyrylcholinesterase; D002802:Cholinesterases