Simplified procedure for the quantitation of radioactive phosphoinositides by thin-layer chromatography

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

This paper describes a method for monitoring enzymatic activity using micellar electrokinetic chromatography (MEKC). MEKC is used to analyze the activity of phosphatidylinositol-specific phospholipase C (PI-PLC) with convenience and precision. PI specific PLC enzyme converts phosphatidylinositol (PI) to diacylglycerol (DAG) and inositol 1,2-cyclic phosphate (IP). The assay system developed is based on monitoring both the breakdown of substrate and the formation of products simultaneously. To obtain the best separation for the substrate PI and product DAG, we investigated changes in concentration of electrolyte buffer and SDS as well as in pH of the electrolyte buffer. Since the structures of the substrate and products are different, the reaction could be monitored easily by MEKC mostly based on hydrophobicity. Under the separation conditions developed, we investigated the enzymatic activity of PI-PLC depending on the concentrations of phosphatidylinositol, various divalent cations and the reaction temperature. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to confirm the molecular masses of the substrate PI and products DAG and IP. The results of this study show that capillary electrophoresis can be widely applied to analyze and characterize many other enzymes since capillary electrophoresis has several advantages as follows, simplicity, speed, no need for radiolabelled substrate, small sample volumes and sufficient accuracy.

Erythrocytes attached to a wheat germ agglutinin coated surface display an altered phospholipid metabolism

Erythrocytes were bound to a lectin-coated surface; the multivalent attachment to this surface resulted in a severe deformation of the cells and an alteration in the cellular phospholipid metabolism. Human erythrocytes were allowed to bind for 20 min at 20 degrees C to polystyrene beads coated with wheat germ agglutinin (WGA beads). The bound erythrocytes were then lysed to produce stroma bound to WGA beads. Control stroma and stroma-WGA beads were incubated at 37 degrees C with gamma-32P-ATP to examine the phospholipid labeling patterns. The control stroma incorporated 32P-label into phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate, in agreement with earlier studies. However, the stroma-WGA beads showed incorporation of 32P-label into phosphatidic acid in addition to that in the phosphoinositides. The quantity of 32P-phosphatidic acid produced during the 20-min assay was 3.23 +/- 0.84 (n = 7) picomoles/micrograms stromal cholesterol; the amount synthesized, however, was dependent on the procedure used to prepare the stroma-WGA beads. If the erythrocytes were bound to the WGA beads at 0 degrees C instead of 20 degrees C, the quantity of 32P-phosphatidic acid produced during the subsequent 37 degrees C assay with gamma-32P-ATP was decreased 4.2 fold; the phosphoinositide labeling pattern was unchanged. In addition, when the time for binding of intact erythrocytes to the WGA beads was varied from 1 to 20 minutes, there was a time-dependent increase in the amount of 32P-phosphatidic acid produced. This induction of phosphatidic acid synthesis could not be duplicated with fluid phase WGA. Therefore, the multivalent binding of intact erythrocytes to WGA beads causes an alteration in phospholipid metabolism.

Phosphatidylinositol 4-phosphate kinase is associated with the membrane skeleton in human erythrocytes

Phosphatidylinositol 4-phosphate kinase was eluted from human erythrocyte stroma by three separate and distinct techniques which are known to disrupt the membrane skeleton. In addition, this kinase was found to be associated with the intact skeletons prepared by Triton X-100 extraction of stroma. Phosphatidylinositol 4-phosphate kinase which has been extracted from the membrane is a freely soluble protein with poor enzymatic activity toward added phosphatidylinositol-4-phosphate; however, the enzyme was shown to reassociate with skeleton-depleted stroma and then regain full enzymatic activity toward stromal bound substrate.