Identification of acylcholine acyl-hydrolase with carboxylic ester-hydrolase in human serum

Species differences in hydrolysis of isocarbacyclin methyl ester (TEI-9090) by blood esterases

Species differences in the hydrolysis of isocarbacyclin methyl ester (TEI-9090) in whole blood and in its separated components were studied in rats, dogs and human. Esterase activity in rat whole blood was approximately 100 and 400 times higher than that in dog and human whole blood, respectively, and was attributed to high plasma activity. In contrast, TEI-9090 hydrolysis activities in dog and human blood were due to red blood cells (RBC), whose activity in humans was slightly suppressed by albumin. In dogs, activity in RBC membranes was 10 times greater than in the cytosol, while in human membrane and cytosol activity was virtually the same. The effects of the esterase inhibitor diisopropylfluorophosphate, bis-p-nitrophenylphosphate (BNPP), eserine, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) and p-chloromercuribenzoate showed that the rat plasma and RBC cytosol esterases hydrolysing TEI-9090 were carboxylesterase (CarbE) and arylesterase (ArE), respectively. The esterases in dog plasma and RBC membrane were CarbE, and RBC cytosol esterase was ArE. In humans, the esterase activities in plasma, RBC membrane and cytosol were butyrylcholinesterase, CarbE and ArE, respectively.

N-oleoyl heparin inhibits the amidolytic activity of plasmin and urokinase

N-desulphated heparin, partially N-acylated on average with three oleoyl chains per molecule, inhibits the amidolytic activity of plasmin (IC50 16 nM) and urokinase (IC50 10mM) when assayed on N-p-tosyl-Gly-Pro-Lys-4-nitroanilide and benzoyl-Ala-Gly-Arg-4-nitroanilide substrates respectively. N-desulphated heparin is not inhibitory. This effect requires the covalent binding of oleoyl residues to heparin and it decreases with increasing concentration of Tris-HCl and non-ionic detergents.

Carboxylesterases in rat and human sera and their relationship of serum aryl acylamidases and cholinesterases

The three enzyme activities, carboxylesterase, aryl acylamidase and cholinesterase activities, have been found in rat and human sera. Rat serum carboxylesterase associated with serum aryl acylamidase activity, but not with serum cholinesterase activity, was purified by ammonium sulfate precipitation, followed by successive chromatographies on DEAE-cellulose, blue Sepharose and QAE-Sephadex, and then electrophoresis. Evidence for the identity of the two enzymes, carboxylesterase and aryl acylamidase, was their co-elution profiles and co-purification in the different steps, including electrophoresis, with constant ratios of specific activities and percentage recoveries. Human serum carboxylesterase associated with serum cholinesterase, purified earlier, was compared with the rat serum esterase. Human serum carboxylesterase and aryl acylamidase activities were inhibited by serotonin and neostigmine, whereas rat serum carboxylesterase and aryl acylamidase activities were not affected by these compounds. Tyramine activated human but not rat aryl acylamidase. Rat and human serum esterase activities were both strongly inhibited by the diisopropylfluorophosphate. Both esterases catalyzed the hydrolysis of short-chain triacylglycerols, such as tributyrin, and medium-chain monoacylglycerols, such as monocaprin, but not the hydrolysis of long-chain triacylglycerols.