Fluorogenic Substrate [Ala-Pro]2-Cresyl Violet But Not Ala-Pro-Rhodamine 110 Is Cleaved Specifically by DPPIV Activity: A Study in Living Jurkat Cells and CD26/DPPIV-transfected Jurkat CellsEmil Boonackera, Sjoerd Elferinka, Abdennasser Bardaia, Bernard Fleischerb, and Cornelis J.F. Van Noordenaa Academic Medical Center, University of Amsterdam, Department of Cell Biology and Histology, Amsterdam, The Netherlands b Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany Correspondence to: Cornelis J.F. Van Noorden, Dept. of Cell Biology and Histology, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands. E-mail: c.j.vannoorden@amc.uva.nl Fluorogenic substrates [Ala-Pro]2-cresyl violet and Ala-Pro-rhodamine 110 have been tested for microscopic detection of protease activity of dipeptidyl peptidase IV (DPPIV) in living cells. DPPIV activity is one of the many functions of the multifunctional or moonlighting protein CD26/DPPIV. As a model we used Jurkat cells, which are T-cells that lack CD26/DPPIV expression, and CD26/DPPIV-transfected Jurkat cells. Ala-Pro-rhodamine 110 is not fluorescent, but after proteolytic cleavage rhodamine 110 fluoresces. [Ala-Pro]2-cresyl violet is fluorescent by itself but proteolytic cleavage into cresyl violet induces a shift to longer wavelengths. This phenomenon enables the simultaneous determination of local (intracellular) substrate and product concentrations, which is important for analysis of kinetics of the cleavage reaction. [Ala-Pro]2-cresyl violet, but not Ala-Pro-rhodamine 110, appeared to be specific for DPPIV. When microscopic analysis is performed on living cells during the first minutes of the enzyme reaction, DPPIV activity can be precisely localized in cells with the use of [Ala-Pro]2-cresyl violet. Fluorescent product is rapidly internalized into submembrane granules in transfected Jurkat cells and is redistributed intracellularly via internalization pathways that have been described for CD26/DPPIV. We conclude that [Ala-Pro]2-cresyl violet is a good fluorogenic substrate to localize DPPIV activity in living cells when the correct wavelengths are used for excitation and emission and images are captured in the early stages of the enzyme reaction. (J Histochem Cytochem 51:959968, 2003) Key Words: living cell cytochemistry, protease, metabolic mapping, biocomplexity, CD26/DPPIV, Jurkat cells, confocal scanning laser, microscopy, fluorescence microscopy
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