TABLE 1.

N-terminal modifications of selected formyl peptides and effects on agonistic activity

Most of the early studies were conducted using neutrophils from rabbits and humans. Note that the concentration of formyl peptides required for superoxide production and enzyme release is 10- to 50-fold higher than the concentration needed for maximal chemotaxis. Therefore, caution should be taken when comparing potency using different assays. Some variations may also exist between assays conducted in different laboratories.

Ligand	Assay	Effects	Potency	References
N-formyl-Met-Leu-Phe	Chemotaxis	Agonistic	pEC50 = 10.15	Freer et al. (1980); Showell et al. (1976)
Met-Leu-Phe	Chemotaxis	Agonistic	pEC50 = 6.17	Showell et al. (1976)
N-acetyl-Met-Leu-Phe	Chemotaxis	Agonistic	pEC50 = 6.70	Freer et al. (1980)
N-p-tolylurea-Met-Leu-Phe	O2− production	Agonistic	pEC50 = 8.70	Higgins et al. (1996)
N-tert-butyloxycarbonyl-Met-Leu-Phe	Enzyme release	Antagonistic	pIC50 = 6.19	Freer et al. (1980)
N-iso-butyloxycarbonyl-Met-Leu-Phe	O2− production	Antagonistic	pIC50 = 6.60	Derian et al. (1996)
N-formyl-Met-Phe-Leu	Chemotaxis	Agonistic	pEC50 = 7.27	Showell et al. (1976)
Met-Phe-Leu	Chemotaxis	Agonistic	pEC50 = 3.62	Showell et al. (1976)
N-acetyl-Met-Nle-Leu-Phe-Phe	Ca2+ flux	Agonistic	pEC50 = 10.00	Gao et al. (1994)
N-formyl-Met-Nle-Leu-Phe-Phe	Ca2+ flux	Agonistic	pEC50 = 10.00	Gao et al. (1994)
Met-Nle-Leu-Phe-Phe	Ca2+ flux	Agonistic	pEC50 = 9.00	Gao et al. (1994)

pIC₅₀, negative logarithm of the IC₅₀; pEC₅₀, negative logarithm of the EC₅₀; pK_d, negative logarithm of K_d.