Determination of enzymatic activity and properties of secretory phospholipase A2 by capillary electrophoresis

Coupling capillary electrophoresis with mass spectrometry for the analysis of oxidized phospholipids in human high-density lipoproteins

The oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (ox-PAPC) products in human high-density lipoproteins (HDLs) were investigated by low-flow capillary electrophoresis-mass spectrometry (low-flow CE-MS). To accelerate the optimization, native PAPC (n-PAPC) standard was first analyzed by a commercial CE instrument with a photodiode array detector. The optimal separation buffer contained 60% (v/v) acetonitrile, 40% (v/v) methanol, 20 mM ammonium acetate, 0.5% (v/v) formic acid, and 0.1% (v/v) water. The selected separation voltage and capillary temperature were 20 kV and 23°C. The optimal CE separation buffer was then used for the low-flow CE-MS analysis. The selected MS conditions contained heated capillary temperature (250°C), capillary voltage (10 V), and injection time (1 s). No sheath gas was used for MS. The linear range for n-PAPC was 2.5-100.0 µg/mL. The coefficient of determination (R2 ) was 0.9918. The concentration limit of detection was 1.52 µg/mL, and the concentration limit of quantitation was 4.60 µg/mL. The optimal low-flow CE-MS method showed good repeatability and sensitivity. The ox-PAPC products in human HDLs were determined based on the in vitro ox-PAPC products of n-PAPC standard. Twenty-one ox-PAPC products have been analyzed in human HDLs. Uremic patients showed significantly higher levels of 15 ox-PAPC products than healthy subjects.

Determination of oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine products in human very low-density lipoproteins by nonaqueous low-flow capillary electrophoresis-mass spectrometry

A simple and fast low-flow capillary electrophoresis-mass spectrometry (low-flow CE-MS) method has been developed to analyze oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (ox-PAPC) products in human very low-density lipoproteins (VLDLs). Native PAPC standard was analyzed to optimize the low-flow CE-MS method. The optimal CE conditions included separation buffer (60% (v/v) acetonitrile, 40% (v/v) methanol, 0.1% (v/v) water, 0.5% (v/v) formic acid, 20 mM ammonium acetate), sheath liquid (60% (v/v) acetonitrile, 40% (v/v) methanol, 0.1% (v/v) water, 20 mM ammonium acetate), separation voltage (20 kV), separation capillary internal diameter (i.d.) (75 µm), separation capillary temperature (23˚C) and sample injection time (6 s). The selected MS conditions included heated capillary temperature (250°C), capillary voltage (10 V), and injection time (1 s). Sheath gas was not used in this study. The total ion chromatograms (TICs), extracted ion chromatograms (EICs) and MS spectra of native PAPC standard and its in vitro oxidation products showed good repeatability and sensitivity. To determine the ox-PAPC products in human VLDLs, the EICs and MS spectra of VLDLs were compared with the in vitro oxidation products of native PAPC standard. For native PAPC standard, the measured linear range was 2.5 - 100.0 µg/mL, and the coefficients of determination (R²) was 0.9994. The concentration limit of detection (LOD) was 0.44 µg/mL, and the concentration limit of quantitation (LOQ) was 1.34 µg/mL. A total of 21 ox-PAPC products were analyzed for the VLDLs of healthy and uremic subjects. The levels of 7 short-chain and 5 long-chain ox-PAPC products on uremic VLDLs were significantly higher than healthy VLDLs. This simple low-flow CE-MS method might be a good alternative for LC-MS for the analysis of ox-PAPC products. Furthermore, it might also help scientists to expedite the search for uremic biomarkers.

Analysis of in vitro oxidized human LDL phospholipids by solid-phase extraction and micellar electrokinetic capillary chromatography

Phospholipids of in vitro oxidized human low-density lipoproteins (LDL) were separated by two different solid-phase extraction (SPE) methods. One of the two methods was designed to test the effects of gradient elution. This SPE method isolated more phospholipids from in vitro oxidized LDL than the other one according to the results of liquid chromatography and electrospray ionization mass spectrometry (LC ESI-MS) analysis. A micellar electrokinetic capillary chromatography (MEKC) method was also used to analyze phospholipids separated by SPE. The results of MEKC and LC ESI-MS were consistent for the major phospholipid classes, including PC, lysoPC, PE, PI and PS. The MEKC profiles showed significant differences for native and oxidized LDL phospholipids. Therefore, the unique combination of SPE and MEKC methods showed dramatic distinctions between native and in vitro oxidized human LDL phospholipids. The combination also shows great potential for rapid analysis of in vivo oxidized human LDL phospholipids in the future.

Metabolism and atherogenic disease association of lysophosphatidylcholine

Lysophosphatidylcholine (LPC) is a major plasma lipid that has been recognized as an important cell signalling molecule produced under physiological conditions by the action of phospholipase A(2) on phosphatidylcholine. LPC transports glycerophospholipid components such as fatty acids, phosphatidylglycerol and choline between tissues. LPC is a ligand for specific G protein-coupled signalling receptors and activates several second messengers. LPC is also a major phospholipid component of oxidized low-density lipoproteins (Ox-LDL) and is implicated as a critical factor in the atherogenic activity of Ox-LDL. Hence, LPC plays an important role in atherosclerosis and acute and chronic inflammation. In this review we focus in some detail on LPC function, biochemical pathways, sources and signal-transduction system. Moreover, we outline the detection of LPC by mass spectrometry which is currently the best method for accurate and simultaneous analysis of each individual LPC species and reveal the pathophysiological implication of LPC which makes it an interesting target for biomarker and drug development regarding atherosclerosis and cardiovascular disorders.

Determination of enzymatic activity by capillary electrophoresis

Enzymes are biological catalysts that play an important role in biochemical reactions necessary for normal growth, maturation and reproduction through whole live world. Their accurate quantitation in biological samples is important in many fields of biochemistry, not only in routine biochemistry and in fundamental research, but also in clinical and pharmacological research and diagnosis. Since the direct measurement of enzymes by masses is impossible, they must be quantified by their catalytic activities. Many different methods have been applied for this purpose so far. Although photometric methods are undoubtedly the most frequently used, separation methods will further gain their position in this field. The article reviews different possibilities for the assay of enzymatic activity by means of capillary electrophoresis (CE). Both the off-line and on-line enzyme assays based on CE are discussed.

Determination of protein phosphorylation by extracellular signal-regulated kinase using capillary electrophoresis and matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Extracellular signal-regulated kinase (ERK) is a key regulatory enzyme mediating cell responses to mitogenic stimulation and is one of the key components in linking growth factor receptor activation to serine/threonine protein phosphorylation processes. Phosphorylation reaction by ERK plays an important role in many signal transduction pathways. ERK phosphorylates numerous substrates such as MBP, microtubule-associated protein 2 (MAP2) and nuclear protein. In particular, MBP is a substrate commonly employed for the detection of ERK activity and contains the consensus primary sequence PRT97P. In this paper, we compared the degree of the phosphorylation reaction of MBP substrate peptides by ERK with the three different MBP substrate peptides, MBP1(KNIVTPRTPPPSQGK), MBP2(VPRTPGGRR) and MBP3(APRTPGGRR) in order to select an efficient substrate peptide for phosphorylation reaction by ERK. The results showed that the MBP3 peptide is the most efficient substrate for phosphorylation reaction by ERK. Using MBP3 peptide, the phosphorylation reaction of MBP by ERK was monitored with both matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and capillary electrophoresis (CE). Our results demonstrate the feasibility of the CE method, the method being a simple and reliable technique in determining and characterizing various kinds of enzyme reaction especially including kinase enzymes.

Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for monitoring the digestion of phosphatidylcholine by pancreatic phospholipase A(2)

Different methods were established for monitoring the phospholipase A(2)(PLA(2)) activity but all of them are rather cumbersome and time consuming. In this paper we have investigated the suitability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the determination of the PLA(2) activity. Phosphatidylcholine (PC) was digested with pancreatic PLA(2) under different conditions, i.e., various Ca(2+), PC, and PLA(2) concentrations. The digestion products were analyzed by MALDI-TOF MS and the concentration of lysophosphatidylcholine (LPC)-generated upon PLA(2) digestion-was determined by the application of an internal standard (known concentration) and by a comparison of their signal-to-noise ratios. The results clearly demonstrate that the LPC concentration determined from the MALDI-TOF mass spectra correlates directly with the activity of the applied enzyme. Additionally, LPC concentration increased with an increase in Ca(2+), as well as in the PC concentration. A single MALDI-TOF mass spectrum provides immediate information on the digestion products as well as on the residual substrate without requirements for any previous derivatization. MALDI-TOF MS can be easily and simply applied for monitoring the PLA(2) activity and we assume that this method might also be useful for other types of phospholipases.

Capillary electrophoretic analysis of mu- and m-calpain using fluorescently labeled casein substrates

Calpains are unique calcium-dependent thiol proteases that have been proposed to participate in a number of physiological processes including signal transduction and protein turnover in skeletal muscle. Calpains exist in two major forms. Interestingly, the two forms of protease show no significant difference in their action on various substrates. The only demonstrable difference in their activity involves the concentration of calcium required for activation. Both mu- and m-calpains typically achieve half maximal activation at 50 microM and 0.7 mM calcium, respectively. The focus of this study was to examine the action of both forms of calpain on casein substrates and assess whether any differences could be observed in the resulting peptide finger print using capillary electrophoresis. Purified mu- and m-calpain were incubated for various lengths of time with Oregon Green labeled alphas- and beta-casein. The reactions were stopped with sodium dodecyl sulfate (SDS) and products separated by capillary electrophoresis in micellar electrokinetic capillary chromatography (MEKC) mode using laser-induced fluorescence (LIF) detection. Comparison of the electropherograms showed no difference in the peptide profile for either enzyme. However, it was found that beta-casein was hydrolyzed more extensively than alphas-casein, by both enzymes. Capillary electrophoresis was found to be a very sensitive technique for detection of calpain activity. Using beta-casein as substrate, the CE approach was able to detect 2-3 ng of calpain activity. The results also suggest that capillary electrophoresis is a useful tool for proteolytic investigations of protein structure.