The purification and structural characterization of phytotoxic lipodepsipeptides from some Pseudomonas syringae pv. syringae strains have been conducted in italy, USA and Japan during the past decade. The main results of the chemical investigations on these metabolites are reported in this paper together with some data of their biological activities. Work on the Phytotoxins produced by strains of the wide host range pathogen Pseudomonas syringae pv. syringae has been pioneered by DeVay and his associates (1,2). They showed that the pathogen produces substances which are phytotoxic and inhibit the growth of a large number of microorganisms. Most of their work was concentrated on two preparations, named syringomycin (SR) (3) and syringotoxin (ST) (4), the first purified from culture filtrates of strains pathogenic on stone fruit, pear and grass hosts, the second produced only by strains from Citrus sp. The peptide nature of these Phytotoxins was also reported. The interesting biological properties of SR and ST prompted us to complete their structural characterization. It was soon demonstrated that preparations supposed to contain pure SR, couid be resolved by RP-HPLC into several components (5). Most of these are structurally related to each other and form a group which was separated from a pair of less polar compounds called syringopeptins (SPs); similarly, ST preparations were shown to contain SPs (6). With an integrated use of FAB-MS, NMR spectroscopy and a combination of chemical and enzymatic methods Ballio, Isogai, Takemoto and their colleagues have at first succeeded in elucidating the structure of the major SR-component (SR-E) (7,8). This compound is a lipodepsinonapeptide with the lipid moiety corresponding to S-hydroxydodecanoic acid; it contains some rare amino acids, among them the previously unknown 4-chlorothreonine (Fig.1) (3). The compiete stereochemistry of the molecule was aiso elucidated (9). Two different isoforms, SR-A1 and SR-G, were reported to differ from SR-E only for the length of the fatty acid moiety (7).

The complete stereochemical structure of syringomycin, a bioactive lipodepsipeptide produced by Pseudomonas syringae pv. syringae, was determined and compared to related phytotoxins.

Syringomycin, a peptide toxin produced by the phytopathogen Pseudomonas syringae pv syringae preferentially stimulated (2-fold) the vanadate-sensitive ATPase activity associated with the plasma membrane of red beet storage tissue. The toxin had a very slight effect on the tonoplast ATPase and had no detectable effect on the mitochondrial ATPase. Optimal stimulation was achieved with 10 to 50 micrograms of syringomycin per 25 micrograms of membrane protein. Treatment of membranes with 0.1% (weight/volume) deoxycholate eliminated the activation effect, and enzyme solubilized with Zwittergent 3-14 was not affected by syringomycin. ATPase activity was activated to the same extent at KCl concentrations ranging from 0 to 50 millimolar. Valinomycin, nigericin, carbonylcyanide p-trifluoromethoxyphenylhydrazone, and gramicidin did not increase the plasma membrane ATPase activity. However, these ionophores did not hinder the ability of syringomycin to stimulate the activity. We suggest that syringomycin does not increase ATPase activity by altering membrane ion gradients nor directly interacting with the enzyme, but possibly through regulatory effectors or covalent modification of the enzyme.

The topography of the photosynthetic reaction center (RC) polypeptides (H, M, and L) was investigated by proteolysis and radioiodination of membrane vesicles isolated from Rhodopseudomonas sphaeroides. Chromatophores, obtained from French-pressed cell lysates, are closed vesicles' and oriented inside out with respect to the cytoplasmic membrane (cytoplasmic side out). Spheroplast-derived vesicles (SDVs), obtained after osmotic lysis of lysozyme-treated cells, are oriented right side in (periplasmic side out). Alpha-Chymotrypsin treatment of chromatophores and trypsin treatment of SDVs resulted in cleavage of H. Alpha-Chymotrypsin treatment of SDVs did not cleave H, and trypsin treatment of chromatophores did not consistently cleave this polypeptide. M and L of both vesicles were apparently not affected by these proteases. The SDV trypsin cleavage product of H was identified by alpha-chymotryptic (125)I-labeled peptide mapping and had a molecular weight of 26 000. Membrane surface radioiodination with chloroglycoluril coated on glass tubes resulted in preferential labeling of H and M of SDVs and chromatophores. The radiospecific activities of H, M, and L were higher with labeling of SDVs as compared to labeling of chromatophores. Alpha-Chymotryptic (125)I-labeled peptide maps of H, M, and L from surface-radioiodinated SDVs differed from the corresponding maps of these polypeptides from surface-radioiodinated chromatophores. The results indicate the asymmetric exposure of H, M, and L on opposite surfaces of the R. sphaeroides membrane. Exposed iodination sites of these polypeptides are more abundant on the periplasmic surface than on the cytoplasmic surface of this membrane.