Characterization of the Isoenzymes of Pig‐Liver Esterase 2. Kinetic Studies

Abstract

The kinetic properties of two of the partially separated isoenzymes I and V of pig liver esterase were studied. The cholinesterase-like isoenzyme I hydrolyses butyrylcholine as well as various other esters and aromatic amides. This isoenzyme is sensitive to 0.01 mM physostigmine and to fluoride. The second type (isoenzyme V) has the features of the so-called aliesterase: it acts preferentially on short-chain aliphatic esters, does not hydrolyse butyrylcholine and has only low activity towards amides. Further differences exist with regard to sensitivity towards organophosphorous inhibitors, to the influence of organic solvents and to the pH optimum. Transacylation reactions with methanol as an acceptor are mainly catalyzed by the isoenzyme of the aliesterase type.The esterase forms I11 and IV, which are located between isoenzymes I and V on the isoelectric focussing column, show kinetic features similar to those of a mixture of I and V. A stepwise increase or decrease, respectively, of certain kinetic properties, e.g. specific activities, is observed for the sequence I, 111, IV, V. A quantitative comparison of the kinetic properties supports our proposed subunit model [l], according to which the main components of these four esterase fractions are the trimers y y y , ayy, m y , and aaa.These results offer explanations for many of the very complex and often controversial results formerly obtained with the heterogeneous pig liver esterase.Kinetic studies on pig liver esterase have been carried out extensively in many laboratories [2 -71.

Purification, characterization and properties of carboxylesterase from the midgut of the silkworm, Bombyx mori L.

“…The product inhibition patterns agree with the Uni-Bi kinetic scheme, with alcohol as the leading product (Hofstee, 1972). Activation observed at low concentrations of p-nitrophenol may be due to the direct reaction of the nucleophilic alcohol with acyl-enzyme intermediate (Junge and Heymann, 1979;Farb and Jencks, 1980) to generate the corresponding aliphatic ester and results in the release of the free enzyme as reported for other esterases.…”

Opinion of the Scientific Panel on food additives, flavourings, processing aids and materials in contact with food (AFC) related to Flavouring Group Evaluation 7 (FGE.07): Saturated and unsaturated aliphatic secondary alcohols, ketones and esters of secon

“…In vitro hydrolysis studies of esters have been performed with specific carboxylesterase isoenzymes isolated from pig and rat livers (Junge & Heymann, 1979;Arndt & Krisch, 1973). The isoenzyme I exhibits an increase in enzyme binding (lower Km) and maximum velocity (Vmax) as the carbon chain length of either the alcohol or carboxylic acid component of the substrate increases.…”

Simulation on the structure of pig liver esterase

“…9 Time history of characteristic atom-atom distances in the active site of the PLE1 monomer during the molecular dynamics run. The black line indicates high stability of the SER204-HIS449 hydrogen bond.…”

“…A further isoenzyme which complements the mutation pattern of PLE3 and PLE5 was described as alternative PLE (APLE) [14]. Determination of the molecular weight has shown that under physiological conditions the enzyme mostly forms trimers which contain a random combination of different isoenzyme monomers [8,9]. 3 In this paper we focus on 3D models for the enzyme structure without deformation by an embedded substrate as a first step towards understanding the reaction mechanism of the enzyme and its enantioselectivity.…”

“…The folding states of parts of the sequence to  and structures were assigned in analogy to known structures of typical , hydrolases [1,7]]. Originally three isoenzymes (, , ) with different sequences and substrate specificities had been characterized in [8,9].…”