Fluorescent chemotactic peptides as tools to identify the f-Met-Leu-Phe receptor on human granulocytes.

Neutrophil functions are initiated within seconds after stimulus addition in response to N-formyl chemotactic peptides and precede ligand-receptor internalization [ 1-51. We have biochemical evidence from subcellular fractionation studies [3, 61 and covalently labelling the receptor by means of a radioiodinated photoactivatable arylazido derivative of the hexapeptide CHO-Nle-Leu-Phe-Nle-Tyr-Lys [ 71 which suggests that internalization of N-formyl peptides proceeds by passage of an occupied receptor in a high-affinity complex from the cell surface to organelles co-sedimenting with the light density Golgi complex. Subsequently, receptors translocate into a granule-rich fraction and N-formyl peptides accumulate in the cytosol. We are now able to visualize continuously, in real-time, the interaction of the fluorescent tetramethylrhodamine (TMR)conjugated derivative of the same N-formyl peptide, TMRpeptide 141, with single human neutrophils by fluorescence microscopy in the presence of excess free peptide, and correlate fluorescence distribution and cell shape.