QUANTITATIVE AND SELECTIVE FLUOROPHORE LABELING OF PHOSPHOSERINE ON PEPTIDES AND PROTEINS - CHARACTERIZATION AT THE ATTOMOLE LEVEL BY CAPILLARY ELECTROPHORESIS AND LASER-INDUCED FLUORESCENCE

Reaction conditions were defined for the selective quantitative deriva tization and fluorophore labeling of phosphoserine residues on peptide s and proteins. Phosphoserine was derivatized with 1,2-ethanedithiol u sing a modification of the reaction conditions defined by R. C. Clark and J. Dijkstra (1987) Int. J. Biochem. 11, 577-585 and H. E. Meyer, E . Hoffmann-Posorke, H. Korte, and M. G. Heilmeyer (1986) FEES Lett. 20 4, 81-66 for stabilizing the phosphoamino acid during Edman degradatio n reactions. Following derivatization, the thiol-serine residues were coupled to fluorescene by iodoacetate reaction. Characterization by ca pillary zone electrophoresis and laser-induced fluorescence allowed qu antitation of phosphoserine content of peptides and proteins at <75 am ol. In three separate experiments, the overall reaction efficiency for 1,2-ethanedithiol derivatization of phosphoserine was estimated at 89 .27 +/- 2.44% (SDM). Subsequent coupling of the derivatized serine res idue with 6-iodoacetamidofluoroscein was estimated at >98% efficiency. Fluorescent probe tagging of phosphoamino acids on proteins and pepti des offers direct quantitative evaluation of cellular phosphorylation states at the attomole level in tissue samples derived from plants, an imals, and humans, without the use of radioisotopes, antibodies, or ma ss spectrometry. (C) 1995 Academic Press,Inc.