title: The identification and characterization of two separate carboxylesterases in guinea-pig serum.
abstract: The esterase activity of guinea-pig serum was investigated. A 3-fold purification was achieved by removing the serum albumin by Blue Sepharose CL-6B affinity chromatography. The partially purified enzyme preparation had carboxylesterase and cholinesterase activities of 1.0 and 0.22 mumol of substrate/min per mg of protein respectively. The esterases were labelled with [3H]di-isopropyl phosphorofluoridate (DiPF) and separated electrophoretically on sodium dodecyl sulphate/polyacrylamide gels. Two main labelled bands were detected: band I had Mr 80 000 and bound 18-19 pmol of [3H]DiPF/mg of protein, and band II had Mr 58 000 and bound 7 pmol of [3H]DiPF/mg of protein. Bis-p-nitrophenyl phosphate (a selective inhibitor of carboxylesterase) inhibited most of the labelling of bands I and II. The residual labelling (8%) of band I but not band II (4%) was removed by preincubation of partially purified enzyme preparation with neostigmine (a selective inhibitor of cholinesterase). Paraoxon totally prevented the [3H]DiPF labelling of the partially purified enzyme preparation. Isoelectrofocusing of [3H]DiPF-labelled and uninhibited partially purified enzyme preparation revealed that there were at least two separate carboxylesterases, which had pI3.9 and pI6.2, a cholinesterase enzyme (pI4.3) and an unidentified protein that reacts with [3H]DiPF and has a pI5.0. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of these enzymes showed that the carboxylesterase enzymes at pI3.9 and pI6.2 corresponded to the 80 000-Mr subunit (band I) and 58 000-Mr subunit (band II). The cholinesterase enzyme was also composed of 80 000-Mr subunits (i.e. the residual labelling in band I after bis-p-nitrophenyl phosphate treatment). The unidentified protein at pI5.0 corresponded to the residual labelling in band II (Mr 58 000), which was insensitive to neostigmine and bis-p-nitrophenyl phosphate. These studies show that the carboxylesterase activity of guinea-pig serum is the result of at least two separate and distinct enzymes.
mesh_terms: D000818:Animals; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000037:antagonists & inhibitors / Q000097:blood*; D002800:Cholinesterase Inhibitors; D002802:Cholinesterases / Q000097:blood; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D007525:Isoelectric Focusing; D007527:Isoenzymes / Q000097:blood*; D007531:Isoflurophate / Q000494:pharmacology; D009388:Neostigmine / Q000494:pharmacology; D009596:Nitrophenols / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D010261:Paraoxon / Q000494:pharmacology
chemical_list: D002800:Cholinesterase Inhibitors; D007527:Isoenzymes; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D007531:Isoflurophate; C008644:nitrophenylphosphate; D009388:Neostigmine; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D002802:Cholinesterases; D010261:Paraoxon