Mitogenic Activity of the Cell Walls of Mycobacteria,Nocardia, Corynebacteria and Anaerobic Coryneforms

The mitogenic activity of the cell walls prepared from Mycobacterium bovis BCG, Nocardia rubra, Corynebacterium diphtheriae PW8, and four species of Propionibacterium, Corynebacterium parvum ATCC 11829, Propionibacterium acnes C7, Propionibacterium granulosum ATCC 25564 and Propionibacterium avidum ATCC 25577, were investigated. These cell walls were active as mitogens on normal spleen cells, anti-θ sera-treated spleen cells, macrophage-depleted spleen cells of C57BL/6J mice and cortisone-treated thymocytes of C57BL/6J mice. It was also shown that these cell walls were mitogenic on spleen cells and macrophage-depleted spleen cells of congenitally athymic (nude) mice. The above results suggest that the cell walls investigated in this study act as mitogens on both thymus-derived lymphocytes (T-cells) and bone marrow-derived lymphocytes (B-cells).     

Splenocytes from tumor-bearing Corynebacterium parvum treated mice maintain interleukin-2 and -3 activity

Summary Systemic and local administration of the bacterium Corynebacterium parvum (more accurately known as Propionibacterium acnes) is reported to exert antitumor action via activated macrophages or short-lived cytotoxic T lymphocytes (CTL), respectively. This study examined the effect of C. parvum treatment on resulting in vitro interleukin levels, which are components in the sequence of events leading to the development of effective CTL. C. parvum administration prevented palpable fibrosarcoma development. This was concomitant with restoration and maintenance of normal interleukin-2 (IL-2) and interleukin-3 (IL-3) levels and prevention of suppressor cell development in mice injected with both tumor cells and vaccine. Our finding of C. parvum-induced maintenance of IL-2 and IL-3 levels and apparent lack of suppressor cell formation lends support to the idea of local C. parvum antitumor action possibly being mediated by CTL arising via the interleukin cascade.     

Competition between cis,trans and Cyclopropane Fatty Acid Formation and its Impact on Membrane Fluidity

The impact of cis, trans and cyclopropane fatty acids on membrane fluidity was investigated using batch‐grown Pseudomonas putida P8 and Comamonas testosteroni ATCC 17454. A major difference observed between the two investigated strains is the absence of the ability to synthesize trans‐unsaturated fatty acids in Comamonas. When grown exponentially at 30 °C, a shift to 35 °C increased the trans/cis ratios of the fatty acids of P. putida P8 from 0 to 0.81 and 0 to 1.07, in lipid extracts and cell hydrolyzates, respectively. After prolonged growth followed by nutrient deprivation for 48 h, both at 30 °C, trans fatty acids were absent, but the cyclo/cis ratios rose from 0.1 to 1.55 in lipid extracts, and from 0.1 to 1.54 in cell hydrolyzates. C. testosteroni ATCC 17454 contained no cyclo fatty acids when harvested in the exponential phase after 6 h, whereas after 72 h cultivation, the cyclo/cis ratios rose to 0.49 and 0.47, in lipid extracts and cell hydrolyzates, respectively. Trans fatty acids were never observed in this strain. Increased cyclo/cis and trans/cis ratios correlated with decreased fluidity measured by the fluorescence anisotropy of 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) intercalated in the bilayers of liposomes and by Fourier Transform Infrared (FTIR) spectroscopy of lipids prepared from the cells. The specific effect of cyclopropane fatty acids on membrane fluidity was much smaller than that of trans fatty acids. FTIR‐measurements of intact cells of P. putida P8 confirmed the high potency of trans fatty acids to decrease the fluidity. In cells with induced cyclopropane fatty acid synthesis, the membranes remained more fluidized, indicating the lower importance of these fatty acids for homeoviscosis.     

Caenorhabditis elegans mounts a p38 MAPK pathway‐mediated defence to Cutibacterium acnes infection

Cutibacterium acnes is capable of inducing inflammation in acne and can lead to a chronic prostatic infection. The diverse pathogenicity among different strains of C. acnes has been presented, but simple appropriate animal models for the evaluation of this bacterium are lacking. In this study, the nematode Caenorhabditis elegans was used as an invertebrate infection model. We revealed that C. acnes type strain ATCC 6919 caused lethal infections to C. elegans in solid and liquid culture media (p < .0001). Compared with the strain ATCC 6919, the antibiotic‐resistant strain HM‐513 was more virulent, resulting in reduced survival (p < .0001). Four different C. acnes strains killed worms with a p value of less than .0001 when provided to C. elegans at 4.8 × 10⁸ CFU/ml. The infection model was also employed to explore host defence responses. An increase in numerous immune effectors in response to C. acnes was detected. We focused on nine C‐type lectins, including: clec‐13, clec‐17, clec‐47, clec‐52, clec‐60, clec‐61, clec‐70, clec‐71 and clec‐227. The induced expression of these C‐type lectin genes was down‐regulated in mutant worms deficient in the p38 mitogen‐activated protein kinase (MAPK) pathway. Meanwhile, PMK‐1 (MAPK) was phosphorylated and activated at the onset of C. acnes infection. By monitoring the survival of mutant worms, we found that PMK‐1, SEK‐1 (MAPKK) and TIR‐1 (MAPKKK) were critical in responding to C. acnes infection. C. elegans pmk‐1 and tir‐1 mutants exhibited higher mortality to C. acnes infection (p < .0001). In conclusion, C. elegans serves as a simple and valuable model to study C. acnes virulence and facilitates improvements in understanding of host innate immune responses.     

Role of respiratory-burst products from polymorphonuclear leukocytes in the antitumor activity of Propionibacterium acnes vaccine

Summary Tumor cells injected into Balb/c mice together with heat-killed 48-h P. acnes cells were rendered nontumorigenic as early as 12 h after injection, as determined by the inability of the tumor cells to give rise to tumors when transferred to a new host. Determination of tumor cell antigen levels by ELISA indicated that the tumor antigens had virtually disappeared by 24 h after injection of tumor cells and P. acnes. In contrast, in control animals injected with tumor cells only, there was an initial drop in tumor antigen levels at 12 h, after which the level rose steadily and tumors developed in 7–10 days. Since the cellular exudate at 12 h was almost entirely composed of polymorphonuclear leukocytes (PMN), we tested the ability of PMN, stimulated by phagocytosis of 48-h P. acnes cells, to produce substances toxic to tumor cells. Results indicated that the supernatant fluid from a phagocytosis mixture of PMN and P. acnes contained material toxic to tumor cells and also to Chinese hamster ovary cells. Tests with scavengers and inhibitors of oxygen-derived radicals suggested that the toxic material is either hydrogen peroxide (H₂O₂) or hydroxyl radicals (OH). Suspensions of 12-h P. acnes, P. acnes cells walls, P. freudenrichii, or latex beads were ineffective in preventing tumor growth, and induced little toxicity when phagocytosed. We conclude that in this test system 48-h P. acnes prevents tumor growth by stimulating the production of toxic oxygen metabolites during phagocytosis by PMN.     

Polyclonal B Cell Activation by Cell Wall Preparations of Gram-Positive Bacteria

The effects of polyclonal B cell activation (PBA) of cell walls and their cell wall fractions obtained from several kinds of gram-positive bacteria were studied using the anti-sheep red blood cell (SRBC) or anti-trinitrophenylated (TNP) SRBC plaque forming cell (PFC) responses of cultured spleen cells from Balb/c, athymic nu/nu, their littermates (nu/+), C3H/He (LPS-responder), C3H/HeJ (LPS-non-responder), (CBA/N × Balb/c) F1 male with an X-linked defect in B cell function and the F1 female mice. The cell walls of Staphylococcus epidermidis (ATCC 155), Lactobacillus plantarum (ATCC 8014), Micrococcus lysodeikticus (NCTC 2665), Mycobacterium rhodochrous (ATCC 184), Streptomyces gardneri (ATCC 23911) and Nocardia corynebacteriodes (ATCC 14898) had the ability to induce polyclonal B cell responses in the spleen cells of Balb/c, nu/nu, nu/+, C3H/He and C3H/HeJ mice. The cell wall fractions prepared by enzymatic digestion from the cell walls of S. epidermidis, S. gardneri or N. corynebacteriodes were also capable of inducing polyclonal B cell responses. The responses of spleen cells from (CBA/N × Balb/c) F1 male mice to these active preparations, except the cell walls of M. rhodochrous, were much lower than those of the F1 female mice. These findings indicate that the majority of the cell wall preparations lacks PBA ability for spleen cells with the CBA/N defect, except for the cell walls of M. rhodochrous which possess this ability. The PBA-ability of synthetic peptidoglycan, muramyl dipeptide (N-acetylmuramyl-L -alanyl-D -isoglutamine, MDP), was also examined, and a similar activity was observed in MDP.     

Esc‐1GN shows therapeutic potentials for acne vulgaris and inflammatory pain

The inflammatory response plays important roles in acne vulgaris and pain pathogenesis. In previous study, Esc‐1GN with anti‐inflammatory, antimicrobial, and lipopolysacchride (LPS) binding activity was identified from the skin of the frog Hylarana guentheri. Here, we report its therapeutic potentials for acne vulgaris and inflammatory pain. Esc‐1GN destroyed the cell membrane of Propionibacteria acnes in the membrane permeability assays. In addition, bacterial agglutination test suggested that Esc‐1GN triggered the agglutination of P. acnes, which was affected by LPS and Ca²⁺. Meanwhile, in vivo anti‐P. acnes and anti‐inflammatory effects of Esc‐1GN were confirmed by reducing the counts of P. acnes in mice ear, relieving P. acnes‐induced mice ear swelling, decreasing mRNA expression and the production of pro‐inflammatory cytokines, and attenuating the infiltration of inflammatory cells. Moreover, Esc‐1GN also displayed antinociceptive effect in mice induced by acetic acid and formalin. Therefore, Esc‐1GN is a promising candidate drug for treatment of acne vulgaris and inflammatory pain.     

Functions of the Clostridium acetobutylicium FabF and FabZ proteins in unsaturated fatty acid biosynthesis

Background  

The original anaerobic unsaturated fatty acid biosynthesis pathway proposed by Goldfine and Bloch was based on in vivo labeling studies in Clostridium butyricum ATCC 6015 (now C. beijerinckii) but to date no dedicated unsaturated fatty acid biosynthetic enzyme has been identified in Clostridia. C. acetobutylicium synthesizes the same species of unsaturated fatty acids as E. coli, but lacks all of the known unsaturated fatty acid synthetic genes identified in E. coli and other bacteria. A possible explanation was that two enzymes of saturated fatty acid synthesis of C. acetobutylicium, FabZ and FabF might also function in the unsaturated arm of the pathway (a FabZ homologue is known to be an unsaturated fatty acid synthetic enzyme in enterococci).     

Effects of salinity on cell growth and docosahexaenoic acid content of the heterotrophic marine microalga Crypthecodinium cohnii

The effects of salinity on cell growth and docosahexaenoic acid (DHA) content of three marine microalgal strains, Crythecodinium cohnii ATCC 30556, C. cohnii ATCC 50051 and C. cohnii RJH were investigated. The lag phases of the three strains increased with increasing salinity in Porphyridium medium. The specific growth rate of C. cohnii ATCC 30556 was the highest at 9 g L⁻¹ NaCl while the other two strains had their highest specific growth rates at 5 g L⁻¹ NaCl. The highest cell dry weight concentrations of 2.51 g L⁻¹ and 1.56 g L⁻¹ were achieved at 9 g L⁻¹ NaCl for C. cohnii ATCC 30556 and ATCC 50051, respectively, while the highest dry weight concentration of 2.49 g L⁻¹ was achieved at 5 g L⁻¹ NaCl for C. cohnii RJH. The highest cell growth yield coefficient on glucose was 0.5 g g⁻¹ for both C. cohnii ATCC 30556 and C. cohnii RJH and 0.45 g g⁻¹ for C. cohnii ATCC 50051. All three strains responded to the change of salinity by modifying their cellular fatty acid compositions. At 9 g L⁻¹ NaCl, C. cohnii ATCC 30556 had the highest total fatty acid content and DHA (C22:6) proportion. In contrast, C. cohnii ATCC 50051 and C. cohnii RJH had the highest DHA content at 5 g L⁻¹ NaCl. C. cohnii ATCC 30556 and ATCC 50051 had the highest DHA yield (131.55 and 68.24 mg L⁻¹ respectively) at 9 g L⁻¹ NaCl while C. cohnii RJH had the highest DHA yield (128.83 mg L⁻¹) at 5 g L⁻¹ NaCl. Received 27 May 1999/ Accepted in revised form 27 August 1999     

Serological changes in adjuvant-treated mice,their specificity and relevance to tumor immunity

Summary The effects of a variety of adjuvant protocols on immunoglobulin levels in normal and tumor bearing CBA mice have been investigated together with their ability to elicit immunoglobulin which bind to tumor cells in vitro and inhibit the growth of a transplanted syngeneic MC-induced fibrosarcoma.A marked increase in serum levels of certain immunoglobulins (especially IgG _2a , IgG _2b and IgM) and immunoglobulin interacting with tumor cells in vitro was noted in normal and tumor bearing mice following the administration of C. parvum (strain No. CN6134 and 10387), P. freudenreichii (strain No. 10470) and B. pertussis while a modest increase in some of these accompanied BCG injection. The Freund's complete and incomplete adjuvant protocols adopted had little effect on any of these parameters. The C. parvum protocols alone inhibited tumor growth.The immunoglobulins evoked by C. parvum strain No. 6134 which bound to tumor cells in vitro were extremely heterogeneous, activity being detected in all Ig classes and subclasses. This organism also evoked immunoglobulins which interacted with syngeneic embryonic fibroblasts, and adult syngeneic kidney and spleen cells.Tumor cells which had been preincubated in sera rich in immunoglobulins binding to tumor cells in vitro (i.e. from C. parvum-treated mice) did not exhibit reduced growth following i.v. or s.c. transplantation to syngeneic recipients.     

Inhibitory and anti‐inflammatory effects of two antimicrobial peptides moronecidin and temporin‐1Dra against Propionibacterium acnes in vitro and in vivo

Proliferation of Propionibacterium acnes (P. acnes) is one of the main pathogenetic mechanisms of acne. Antimicrobial peptides with low‐drug resistance and nonresidual are potential anti‐acne agents. In this study, two antimicrobial peptides named temporin‐1Dra and moronecidin were synthesized and tested their antimicrobial activity against P. acnes in vitro and in vivo. These two peptides inhibited the growth of Escherichia coli, Staphylococcus aureus, Candida albicans, and P. acnes. The minimal inhibitory concentrations (MICs) of temporin‐1Dra and moronecidin to P. acnes were 30 and 10 μM, respectively. Both peptides exhibited strong resistance to heat and pH, but no obvious cytotoxicity to HaCaT cells. They also displayed persistent antimicrobial activities in the microbial challenge test. In the P. acnes‐induced inflammation mouse model, moronecidin significantly decreased the ear swelling thickness in a concentration‐dependent manner. At the 14th day after injection, 20 μg/day moronecidin reduced the ear swelling thickness to 46.15 ± 5.23% compared with the normal cream group. Tissue staining showed that moronecidin effectively reduced abscess and thickness of the dermis layer. Our results indicate that the antimicrobial peptide moronecidin could be developed as a potential natural anti‐acne agent in the cosmetics or pharmaceutical industries.     

Fatty Acids of Myxococcus xanthus

Fatty acids were extracted from saponified vegetative cells and myxospores of Myxococcus xanthus and examined as the methyl esters by gas-liquid chromatography. The acids consisted mainly of C₁₄ to C₁₇ species. Branched acids predominated, and iso-pentadecanoic acid constituted half or more of the mixture. The other leading component (11–28%) was found to be 11-n-hexadecenoic acid. Among the unsaturated acids were two diunsaturated ones, an n-hexadecadienoic acid and an iso-heptadecadienoic acid. No significant differences between the fatty acid compositions of the vegetative cells and myxospores could be detected. The fatty acid composition of M. xanthus was found to be markedly similar to that of Stigmatella aurantiaca. It is suggested that a fatty acid pattern consisting of a large proportion of iso-branched C₁₅ and C₁₇ acids and a substantial amount of an n-16:1 acid is characteristic of myxobacteria.     

Purification and structure analysis of mycolic acids in <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>

Corynebacterium glutamicum is widely used for producing amino acids. Mycolic acids, the major components in the cell wall of C. glutamicum might be closely related to the secretion of amino acids. In this study, mycolic acids were extracted from 5 strains of C. glutamicum, including ATCC 13032, ATCC 13869, ATCC 14067, L-isoleucine producing strain IWJ-1, and L-valine producing strain VWJ-1. Structures of these mycolic acids were analyzed using thin layer chromatography and electrospray ionization mass spectrometry. More than twenty molecular species of mycolic acid were observed in all 5 strains. They differ in the length (20–40 carbons) and saturation (0–3 double bonds) of their constituent fatty acids. The dominant species of mycolic acid in every strain was different, but their two hydrocarbon chains were similar in length (14–18 carbons), and the meromycolate chain usually contained double bonds. As the growth temperature of cells increased from 30°C to 34°C, the proportion of mycolic acid species containing unsaturated and shorter hydrocarbon chains increased. These results provide new information on mycolic acids in C. glutamicum, and could be useful for modifying the cell wall to increase the production of amino acids.     

Unsaturated Fatty Acids Promote the Phagocytosis of P. aeruginosa and R. equi by RAW264.7 Macrophages

In the present study, using the murine monocyte/macrophage cell line RAW264.7 as a model system, we analyzed the phagocytosis rate and the bactericidal capacity of polyunsaturated fatty acids (PUFA)-enriched macrophages against Pseudomonas aeruginosa and Rhodococcus equi. The P. aeruginosa strain ATCC 10145, the virulent R. equi strain ATCC 33701, and the non-virulent R. equi strain ATCC 6939 were examined. Flow cytometric detection of intracellular microorganisms in combination with viability assays were used to determine the impact of PUFA on the number of engulfed, surviving as well as replicating bacteria. Macrophage enrichment with PUFA resulted in an increase of the internalization rate of the microorganisms by the immune cells. Moreover, an impeding action of the unsaturated fatty acids on the intracellular survival rates of the virulent strains P. aeruginosa ATCC 10145 and R. equi ATCC 33701 could be observed. The n-3 fatty acid docosahexaenoic acid (DHA) as well as the n-6 fatty acid arachidonic acid (AA) showed the most pronounced effects. Taken together, our data support the idea of supplementing PUFA to immunocompromised individuals as well as to people suffering from chronic infections with P. aeruginosa or R. equi to improve macrophage phagocytic and microbicidal activity.     

Effects of medium composition on the growth and lipid production of microplasmodia of Physarum polycephalum

Physarum polycephalum is a plasmodial slime mold. One of the trophic stages in the life cycle of this organism is a plasmodium. In submerged culture, plasmodia are fragmented into microplasmodia. The latter both lack cell walls and are capable of rapid growth. There has been limited information on the effects of medium composition on the growth and lipid accumulation of microplasmodia. In this study, optimization of medium components by response surface methodology showed that tryptone and yeast extract concentrations had the most significant effects on lipid and biomass production; significant synergistic interactions between glucose and tryptone concentration on these responses were also recorded. The optimal medium was composed of 20 g/L of glucose, 6.59 g/L of tryptone, and 3.0 g/L of yeast extract. This medium yielded 13.86 g/L of dry biomass and 1.97 g/L of lipids. These amounts are threefold higher than those of the American Type Culture Collection (ATCC) medium. In addition, biomass and lipid production reached maximal values between only 4 and 5 days. Fatty acid compositions analysis by gas chromatography-mass spectrometer (GC–MS) revealed that P. polycephalum lipids consisted mainly of oleic acid (40.5%), linoleic acid (10%), and octadecynoic (15.8%). This is the first report on the fatty acid composition of P. polycephalum microplasmodia. These results suggest that the biomass of microplasmodia could be used as a source of material for direct conversion into biodiesel because of the absence of cell walls or it could also be used as a supplemental source of beneficial fatty acids for humans, albeit with some further evaluation needed.     

Allelopathic Effects of Toxic Haptophyte <Emphasis Type="Italic">Prymnesium parvum</Emphasis> Lead to Release of Dissolved Organic Carbon and Increase in Bacterial Biomass

The haptophyte Prymnesium parvum has lytic properties, and it affects coexisting phytoplankton species through allelopathy. We studied the effect of P. parvum allelochemicals on the lysis of the nontoxic and nonaxenic cryptomonad Rhodomonas salina and the consequent release of dissolved organic carbon (DOC). Changes in production, cell density, and biomass of associated bacteria were measured over 12 h. Six different combinations of P. parvum and R. salina cultures, their cell- and bacteria-free filtrates, and growth media as controls were used in the experiments. When P. parvum and R. salina cells were mixed, a significant increase in DOC concentration was measured within 30 min. Bacterial biomass increased significantly during the next 6 to 12 h when R. salina was mixed either with the P. parvum culture or the cell-free P. parvum filtrates (allelochemicals only). In contrast, bacterial biomass did not change in the treatments without the allelopathic action (without R. salina cells). Blooms of P. parvum alter the functioning of the planktonic food web by increasing carbon transfer through the microbial loop. In addition, P. parvum may indirectly benefit from the release of DOC as a result of its ability to ingest bacteria, by which it can acquire nutrients during limiting conditions.     

Characterization of β-1,3-galactosyl-<Emphasis Type="Italic">N</Emphasis>-acetylhexosamine phosphorylase from <Emphasis Type="Italic">Propionibacterium acnes</Emphasis>

Homologs of the β-1,3-galactosyl-N-acetylhexosamine phosphorylase (GalHexNAcP) gene (gnpA) were cloned from the genomic DNA of Propionibacterium acnes JCM6425 and P. acnes JCM6473, showing 99.9% and 97.9% nucleotide sequence identity, respectively, with the ppa0083 gene from the genome-sequenced P. acnes KPA171202. No gnpA gene was detected in the genomic DNA of type strain P. acnes ATCC25746. The recombinant enzyme from P. acnes JCM6425 (GnpA) showed approximately 70 times higher specific activity of phosphorolysis on galacto-N-biose (Galβ1→3GalNAc, GNB) than that on lacto-N-biose I (Galβ1→3GlcNAc). K _m value for GnpA on GNB was high, but GnpA did not exhibit activity on any derivatives of GNB examined. These results indicate that GnpA is GalHexNAcP which should be classified as galacto-N-biose phosphorylase. The large k _cat value of GnpA on GalNAc suggests that GnpA would be a useful catalyst for the synthesis of GNB.     

Growth-Promoting Effects of Fatty Acids on Excised Wheat Roots and Oat Coleoptiles

The growth action of some fatty acids and alcohols with carbon number from 1 to 4 was tested on excised wheat roots in aseptic cultures. Growth, cell length, and dry weight were measured after seven days. The tested substances were: Formic acid, acetic acid, propionic acid, n-Butyric acid, isobutyric acid, acelaldehyde, propionaldohyde, ethanol, n-propanol, isopropanol, n-butanoL and isobutanol. The primary alcohols and all of the acids, except formic acid, promoted the cell elongation and the total growth, but the meristematic activity was inhibited in the higher concentrations. The concentrations with maximal growth-promoting activity were 10^?2M to 10^?3M for the alcohols and 10^?4M for the acids. Propionic acid was applied in darkness, red light, and white light and proved to increase the cell length from 215 μ, 180 μ, and 120 μ up to 240 μ in all three treatments. The growth rate was not affected, but the duration of the cell elongation was extended. The presence of iron proved to be necessary for the stimulation. The chlorophyll content in the light grown roots was relatively unaffected when the cell length was increased and the dry weight was not increased as long the cell number was normal. The growth of Avena coleoptile segments was slightly promoted by propionic acid in the presence of IAA.     

Purification and characterization of elicitor-induced lipoxygenase in tobacco cells

Lipoxygenase activity was induced in a tobacco cell suspension culture by treatment with glycopeptide elicitors prepared from the cell walls of Phytophthora parasitica var, nicotianae, and in tobacco seedlings infected by this fungal pathogen. Upon purification and characterization, the enzyme appeared to have a molecular weight of 96000, a pl of 5.1 and a K_m of 20.9 μM with linoleic acid as substrate. According to its acidic optimum pH, it belongs to type-2 lipoxygenases. Using linoleic, linolenic and arachidonic acids as substrates, the products formed in vitro by lipoxygenase were characterized. 9- and 5-hydroperoxides were the main products obtained from the C₁₈ and C₂₀ fatty acids, respectively, thereby indicating that a 5-lipoxygenase accounts for most of the elicitor-induced activity, since the main site of insertion of molecular oxygen is on C-5 of arachidonic acid. Small amounts of 13-hydroperoxides were also formed from the C₁₈ fatty acids. In vitro, the strongest inhibitors of tobacco lipoxygenase were n-propylgallate and nordihydroguaiaretic acid. The possible involvement of this enzyme in signaling phenomena leading to defense induction in plants via jasmonic acid and other fatty acid-derived products is discussed.