Neutral endopeptidase activity in the interaction of N-formyl-L-methionyl-L-leucyl-L-phenylalanine with human polymorphonuclear leukocytes

Abstract

Human polymorphonuclear leukocytes (PMN) hydrolyze the synthetic chemoattractant N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe) at nanomolar concentrations in an autocatalytic-like manner that deviates from classical Michaelis-Menten kinetics [Yuli, I. & Snyderman, R. (1986) J. Biol. Chem. 261, 4902-4908]. By using inhibitors of distinct classes of endoproteases, this particular fMet-Leu-Phe degradation was attributed exclusively to an exoplasmic metalloendoprotease that matches the ubiquitous neutral endopeptidase (NEP). Membrane-bound NEP hydrolyzes non-chemotactic substrates according to a classic Michaelis-Menten mechanism. By competitive inhibition with non-chemotactic substrates, fMet-Leu-Phe was found to interact with membrane NEP through a single active site, in a non-cooperative mode with an apparent Km in the order of 1 mM. The discrepancy between the ordinary hydrolysis of the micromolar and millimolar concentrations of fMet-Leu-Phe, reported by others, and the particular degradation of the nanomolar fMet-Leu-Phe, could not be accounted for by any coherent correlation between NEP activity/inhibition and modulation of fMet-Leu-Phe binding to its receptor, and/or induction of fMet-Leu-Phe-receptor-mediated inflammatory responses. Based on these and previously reported results, a novel model is proposed in which the fMet-Leu-Phe-induced inflammatory stimulation of PMN involves both NEP and the fMet-Leu-Phe receptor. By this model, NEP and the fMet-Leu-Phe receptor are distinct membrane entities which can form dynamic binary and tertiary complexes; thus accounting for the unusual kinetic features of fMet-Leu-Phe degradation, as well as the two receptor states. The complex of NEP and the fMet-Leu-Phe receptor might be conceived as a chemotactic-perception mechanism that combines the high affinity of the receptor and the rapid turnover of NEP.