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	$\text{[math]}$ 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	$\text{[math]}$ 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