Application of capillary electrophoresis to determination of enzyme activity and other properties of phosphatidylinositol-specific phospholipase C

Separation of fluorescently labeled phosphoinositides and sphingolipids by capillary electrophoresis

Phosphoinositides (PIs) and sphingolipids regulate many aspects of cell behavior and are often involved in disease processes such as oncogenesis. Capillary electrophoresis with laser induced fluorescence detection (CE-LIF) is emerging as an important tool for enzymatic assays of the metabolism of these lipids, particularly in cell-based formats. Previous separations of phosphoinositide lipids by CE required a complex buffer with polymer additives which had the disadvantages of high cost and/or short shelf life. Further a simultaneous separation of these classes of lipids has not been demonstrated in a robust buffer system. In the current work, a simple separation buffer based on NaH(2)PO(4) and 1-propanol was optimized to separate two sphingolipids and multiple phosphoinositides by CE. The NaH(2)PO(4) concentration, pH, 1-propanol fraction, and a surfactant additive to the buffer were individually optimized to achieve simultaneous separation of the sphingolipids and phosphoinositides. Fluorescein-labeled sphingosine (SFL) and sphingosine 1-phosphate (S1PFL), fluorescein-labeled phosphatidyl-inositol 4,5-bisphosphate (PIP2) and phosphatidyl-inositol 3,4,5-trisphosphate (PIP3), and bodipy-fluorescein (BFL)-labeled PIP2 and PIP3 were separated pairwise and in combination to demonstrate the generalizability of the method. Theoretical plate numbers achieved were as high as 2×10(5) in separating fluorophore-labeled PIP2 and PIP3. Detection limits for the 6 analytes were in the range of 10(-18)-10(-20)mol. The method also showed high reproducibility, as the relative standard deviation of the normalized migration time for each analyte in the simultaneous separation of all 6 compounds was less than 1%. The separation of a mixture composed of diacylglycerol (DAG) and multiple phosphoinositides was also demonstrated. As a final test, fluorescent lipid metabolites formed within cells loaded with BFLPIP2 were separated from a cell lysate as well as a single cell. This simple and robust separation method for SFL and S1PFL and various metabolites of phosphoinositide-related signal transduction is expected to enable improved enzymatic assays for biological and clinical applications.

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.

Separation of phospholipids in microfluidic chip device: application to high-throughput screening assays for lipid-modifying enzymes

Phospholipid molecules such as ceramide and phosphoinositides play crucial roles in signal transduction pathways. Lipid-modifying enzymes including sphingomyelinase and phosphoinositide kinases regulate the generation and degradation of these lipid-signaling molecules and are important therapeutic targets in drug discovery. We now report a sensitive and convenient method to separate these lipids using microfluidic chip-based technology. The method takes advantage of the high-separation power of the microchips that separate lipids based on micellar electrokinetic capillary chromatography (MEKC) and the high sensitivity of fluorescence detection. We further exploited the method to develop a homogenous assay to monitor activities of lipid-modifying enzymes. The assay format consists of two steps: an on-plate enzymatic reaction using fluorescently labeled substrates followed by an on-chip MEKC separation of the reaction products from the substrates. The utility of the assay format for high-throughput screening (HTS) is demonstrated using phospholipase A(2) on the Caliper 250 HTS system: throughput of 80min per 384-well plate can be achieved with unattended running time of 5.4h. This enabling technology for assaying lipid-modifying enzymes is ideal for HTS because it avoids the use of radioactive substrates and complicated separation/washing steps and detects both substrate and product simultaneously.

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.

Cyclodextrin-mediated micellar electrokinetic chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the enantiomer separation of racemorphan in human urine

Micellar electrokinetic chromatography (MEKC) was successfully and conveniently applied to the chiral separation with the addition of cyclodextrins (CDs) as chiral selector to the running buffer. Chiral separation depended on the type of CD; in particular, beta-CD was effective for the chiral separation of racemorphan. We investigated the optimal conditions of type and concentration of CD as chiral selector for the routine enantiomeric separation of racemorphan with good reproducibility. The effects of other parameters such as buffer pH and detection wavelength were also investigated to obtain the optimum conditions for the enantiomeric separation of racemorphan. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used for confirmation of racemorphan. The optimal conditions for enantiomeric separation of the racemorphan were as follows: 50 mM borate buffer at pH 9.4 with 50 mM SDS, 10 mM beta-CD and 20% 1-propanol, 57 cm x 50 microns fused-silica capillary column, and UV detection at 192 nm. Based on the developed method, racemorphan in human urine was also separated and determined using solid-phase extraction and MEKC.

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

A capillary electrophoretic (CE) system coupled with a diode array UV detector was used for the assay of secretory phospholipase A2 (sPLA2) activity. This method is based on monitoring both the breakdown of substrates and the formation of products simultaneously using micellar electrokinetic chromatographic techniques. Under our developed separation conditions, we analyzed the substrates and products quantitatively, and investigated enzyme activity as a function of reaction time and presence of enzyme activator or inhibitor. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was also utilized to confirm the phosphatidylcholine, a substrate of sPLA2. In order to test the feasibility of the developed method for measurement of enzymatic activity, we compared it to the conventional radioactive assay method for sPLA2. On the basis of our results, the conventional method can be complemented, or even replaced, by this new CE method which possesses the advantages of short analysis time, use of non-radiolabeled and inexpensive substrates, simple measurement of enzymatic activity, and exact quantitation of substrate and product.

Advances in capillary electrophoresis

This review summarizes the advancement in operational modes and selected applications of the title technique over the past five years. Regarding operational modes particular emphasis is put upon increasing selectivity and resolution, hyphenation of capillary electrophoresis with techniques based on other than electromigration principles, the so-called chip technology and new ways of detection. In applications selected examples of chiral separation and separation of biopolymers (proteins, nucleic acids) are emphasized. It is demonstrated that capillary electrophoresis represents a complementary technique to high-performance column chromatography and in a number of cases it offers better separations than standard chromatographic procedures.