Identification of a secretory phospholipase A2 from Papaver somniferum L. that transforms membrane phospholipids

The full-length sequence of a new secretory phospholipase A2 was identified in opium poppy seedlings (Papaver somniferum L.). The cDNA of poppy phospholipase A2, denoted as pspla2, encodes a protein of 159 amino acids with a 31 amino acid long signal peptide at the N-terminus. PsPLA2 contains a PLA2 signature domain (PA2c), including the Ca(2+)-binding loop (YGKYCGxxxxGC) and the catalytic site motif (DACCxxHDxC) with the conserved catalytic histidine and the calcium-coordinating aspartate residues. The aspartate of the His/Asp dyad playing an important role in animal sPLA2 catalysis is substituted by a serine residue. Furthermore, the PsPLA2 sequence contains 12 conserved cysteine residues to form 6 structural disulfide bonds. The calculated molecular weight of the mature PsPLA2 is 14.0 kDa. Based on the primary structure PsPLA2 belongs to the XIB group of PLA2s. Untagged recombinant PsPLA2 obtained by expression in Escherichia coli, renaturation from inclusion bodies and purification by cation-exchange chromatography was characterized in vitro. The pH optimum for activity of PsPLA2 was found to be pH 7, when using mixed micelles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Triton X-100. PsPLA2 specifically cleaves fatty acids from the sn-2 position of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and shows a pronounced preference for PC over phosphatidyl ethanolamine, -glycerol and -inositol. The active recombinant enzyme was tested in vitro against natural phospholipids isolated from poppy plants and preferably released the unsaturated fatty acids, linoleic acid and linolenic acid, from the naturally occurring mixture of substrate lipids.

Hemolysis as a Factor in Clinical Chemistry and Hematology of the Dog

Serum biochemical, hemostatic, and hematologic analytes were determined by four laboratories on dog serum or plasmas containing increasing amounts of hemolysate. From the results of testing, interferographs were prepared to aid in decision making and to enhance visualization of the effects of hemolysis on the determination of the analytes. Heniktsus consistently interfered with the analysis of creatinine phosphokinase, lactic dehydrogenase, aspartate aminotransferase, lipase, and albumin, all of which appeared to increase with increasing hemolysis. The results for the remainder of the biochemical, hemostatic, and hematologic analytes varied greatly among analyzers or methods, rarely in a predictable manner, indicating that each laboratory should evaluate the effects of hemolysis on each analyzer and for each method used, in order to make informed decisions on the use of hemolyzed but irreplaceable samples.

Modified photometric method for the determination of phospholipase A activities

A modified photometric method for the determination of phospholipase A activities which is based on a previously published reaction principle is described. The modified assay uses a lyophilized substrate emulsion rather than a freshly prepared phospholipid emulsion and a new chromogen (tribromohydroxybenzoic acid and 4-amino-antipyrine) with a high molar absorption coefficient (1,930 m2/mol at 546 nm, 2,900 m2/mol at 512 nm wavelength). The new test is more practicable with respect to pipetting volumes and incubation times. Preliminary results of a method evaluation indicate that the modified assay fulfills the usual criteria for clinical chemical enzyme measurements.

An enzymatic colorimetric assay of calcium-dependent phospholipases A

In this paper we describe a new method for the assay of calcium-dependent phospholipases A. In this method released fatty acids are quantitated by an enzymatic colorimetric reagent kit which is commercially available. We have tested the applicability of this assay with enzymes from porcine pancreas (phospholipase A2), snake venom (phospholipase A2), and Rhizopus arrhizus (a lipase with phospholipase A1-like activity) as well as with a phospholipase A2 activity of bovine seminal vesicle fluid. We conclude that the kit procedure is a convenient, rapid and sensitive endpoint assay for calcium-dependent phospholipases A.