Casein-derived peptides can modulate the production of 5-hydroxyeicosatetraenoic acid in human neutrophils.

The effects of peptides derived from bovine casein hydrolysates were evaluated on oxygen-free radical release, 5-hydroxyeicosatetraenoic acid (5-HETE), and leukotriene B4 (LTB4) production by human polymorphonuclear leukocytes (PMNs). PMNs were activated by N-formyl-methionyl-leucyl-phenylalanine, phorbol myristate acetate, calcium ionophore (A23187), or opsonized zymosan. Tyrosyl-prolyl-phenylalanyl-proline (fragment 60-63 from bovine beta-casein) inhibited oxygen-free radical production and 5-HETE production but had no effect on the production of LTB4 and LTB4 isomers.

Boomerang effect between [Met]-enkephalin derivatives and human polymorphonuclear leukocytes.

[Met]-enkephalin or its precursor, pre-[Met]-enkephalin, were exposed to activated oxygen species produced by human phorbol myristate acetate (PMA)-stimulated polymorphonuclear leukocytes (PMNs) and then analyzed by high-pressure liquid chromatography (HPLC). The chromatograms recorded at the tyrosine maximum wavelength (lambda em 300 nm and lambda ex 280 nm) showed the formation of new peptides by oxidation of methionyl residue in position 5 and ortho, meta, or para hydroxylation of phenylalanyl residue in position 4. The chromatograms recorded at the dityrosine maximum wavelength (lambda em 400 nm and lambda ex 325 nm) showed the formation of new dimeric peptides which contained two [Met]-enkephalin-derivatives linked by a dityrosyl group.

Neutrophil-catalysed dimerisation of tyrosyl peptides.

Evidence is given that tyrosyl-peptides are dimerised by polymorphonuclear leukocytes leading to a new family of compounds. The products formed are homo- and hetero-dimeric peptides with linkage between the tyrosyl residues. This corresponds to a dityrosine structure as determined by analytic and spectroscopic data.