Fluorescence-labeled peptides as isoelectric point (pI) markers in capillary isoelectric focusing with fluorescence detection.

Commercially available peptides, mostly angiotensin derivatives, were labeled at their N-terminal amino group with 5-carboxytetramethylrhodamine succinimidyl ester, to obtain fluorescent pI markers for capillary isoelectric focusing with fluorescence detection. The labeled peptides were purified by reversed-phase chromatography. They were well separated on isoelectric focusing in a polyacrylamide gel slab and their pIs were determined by comigration with protein-pI markers. The fluorescent markers could be detected as sharp peaks in capillary isoelectric focusing with laser-induced fluorescence detection (He-Ne laser, 1 mW, 543.5 nm). The detection limit was found to be around 3 x 10(-12) M (0.8 amol). Tetramethylrhodamine-labeled pea lectin (3 pg) was subjected to capillary isoelectric focusing and the pIs of the fluorescent derivatives of the lectin were determined by using the fluorescence-labeled peptides as pI markers.