Two major azoverdins were isolated from the cultures of Azomonas macroo'togenes ATCC 12334 grown in irondeficient medium. Their structures have been established using fast atom bombardment-mass spectroscopy, homonuclear and heteronuclear two-dimensional 15N, 13C and IH NMR, and circular dichroism techniques. These siderophores are chromopeptides possessing at the N-terminal end of their peptide chain the chromophore derived from 2,3-diamino-6,7-dihydroxyquinoline common to pyoverdins. The linear peptide chain (L)-Hse--(D)-AcOHOrn-(D)-Ser-(L)-AcOHOrn-(D)-Hse-(L)-CTHPMD has at its C-terminal end a new natural amino acidwhich is the result of the condensation of I mol of homoserine and 1 mol of 2,4-diaminobutyric acid forming a cyclic amidine belonging to the tetrahydropyrimidine family: 2-homoseryl-4-carboxyl-3,4,5,6-tetrahydropyrimidine. The azoverdins differ only by a substitutent bound to the nitrogen on C-3 of the chromophore: azoverdin, the most abundant one, possesses a succinamide moiety, whereas azoverdin A bears a succinic acid moiety, lSN-labelled azoverdin afforded readily, after the complete assignment of the ISN spectrum of the siderophore, a sequence determination of the peptidic part of the molecule and gave evidence for the presence of two tetrahydropyrimidine groups on the molecule: one on the chromophore and the second at the C-terminal end of the siderophore.

In order to identify and characterize the receptors involved in pyoverdin-mediated iron transport in Pseudomonas aeruginosa ATCC 15692, a photoactivatable siderophore has been synthesized. In the dark, this probe is stable and is able to promote iron transport at the same rate as the native pyoverdin. Under irradiation at 312 nm, the molecule is photodecomposed and a clear inhibition of the iron transport is observed. With the radioactive form of this photoactivatable probe, we were able to visualize on a SDS-PAGE gel a labelled protein of approximately 90 kDa molecular mass, which is very likely the FpvA receptor or a yet unknown pyoverdin receptor.