- Evaluation of snake venom phospholipase A2: Hydrolysis of non-natural esters
-
Phospholipase A2 from the rattlesnake Crotalus durissus terrificus was employed for the first time to test its enantioseletivity on the hydrolysis of different non-natural esters. It was observed that the structure of this small enzyme is restrictive in the choice of its lipase action with non-natural substrates. Two forms of the enzyme were used; free and as its cross-linked enzyme aggregate (CLEA). With all substrates, the free enzyme showed activity similar to the CLEA preparation. The advantage of the CLEA phospholipase is the possibility to reuse it in several consecutive reactions without a decrease of activity and selectivity with good but higher yields and ee than with the free enzyme.
- Pirolla, Renan A. S.,Baldasso, Paulo A.,Marangoni, Se?rgio,Moran, Paulo J. S.,Rodrigues, Jose? Augusto R.
-
experimental part
p. 300 - 307
(2011/10/05)
-
- A New Class of Phospholipase A2 Substrates: Kinetics of the Phospholipase A2 Catalyzed Hydrolysis of 3-(Acyloxy)-4-nitrobenzoic Acids
-
3-(Acyloxy)-4-nitrobenzoic acids were synthesized with acyl groups ranging from butyryl to dodecanoyl.All these compounds yielded monomeric solutions in water with 1.6percent (v/v) acetonitrile in the neutral pH range, and they were hydrolyzed by catalytic amounts of phospholipases A2 from a variety of sources as shown by the spectral change at 425 nm due to the appearance of nitrophenolate ion.Most of the kinetic studies were performed using Agkistrodon piscivorus piscivorus phospholipase A2, but similar results were obtained with porcine pancreatic and Crotalus atrox phospholipase A2.The catalytic reaction requires the presence of Ca2+, but unlike the hydrolysis of lecithins, the hydrolysis of these substrates also occurs in the presence of Ba2+ and Sr2+, while Mg2+ and Zn2+ are not catalytically competent.Increasing the acyl chain length increases the enzymatic rate mainly by enhancing the hydrophobic interaction in the E-Ca2+-S complex.Among structural isomers of the octanoyl compound, 3-nitro-4-(octanoyloxy)benzoic acid shows the highest specificity toward the enzyme, suggesting that it is in this compound that the distance between the negatively charged carboxylate and the reactive ester approximates best that found in the lecithin-enzyme complex.All kinetic characteristics of the enzymatic hydrolysis indicate that the reaction occurs by the same mechanism as that of the hydrolysis of lecithins.The highest catalytic efficiency observed with this series of substrates occurs with 3-dodecanoyl-4-nitrobenzoic acid, and the second-order rate constant of this reaction (kcat/Km = 9.1 x 1E+4 M-1 s-1) is only 1 order of magnitude lower than that of the hydrolysis of egg phosphatidylcholine in unilamellar vesicles.The reactivity of all isomers, especially that of the p-carboxy ester, shows that Ca2+ does not act as a catalyst in the phospholipase A2 catalyzed hydrolysis but rather serves to bind and orient the substrate at the active site of the enzyme.The octanoyl compounds, 1 and 2, are ideally suited for a rapid and sensitive spectrophotometric assay of phospholipases A2, and the conditions for the assay are described.
- Cho, Wonhwa,Markowitz, Michael A.,Kezdy, Ferenc J.
-
p. 5166 - 5171
(2007/10/02)
-
- THE SUBSTRATE SPECIFICITY OF PHOSPHOLIPASE A2 : THE REACTION OF THE ENZYME WITH 3-OCTANOYLOXY-4-NITROBENZOIC ACID
-
3-Octanoyloxy-4-nitrobenzoic acid is hydrolyzed by the phospholipase A2(D-49) from the venom of Agkistrodon piscivorus.The hydrolytic reaction is truly catalytic, requiring the presence of calcium ion (Kd=3.3 +/- 0.7mM).At pH=7.0 the value of the enzymatic rate constant is (Kcat/Km)max=175 +/- 14 M-1 sec-1, comparable to that of the enzymatic hydrolysis of 3-sn-dibutyryl lecithin.
- Markowitz, Michael A.,Seykora, John T.,Kezdy, F. J.
-
p. 1033 - 1038
(2007/10/02)
-