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Hexose Oxidase-Mediated Hydrogen Peroxide as a Mechanism for the Antibacterial Activity in the Red Seaweed Ptilophora subcostata.

ABSTRACT: Marine algae have unique defense strategies against microbial infection. However, their mechanisms of immunity remain to be elucidated and little is known about the similarity of the immune systems of marine algae and terrestrial higher plants. Here, we suggest a possible mechanism underlying algal immunity, which involves hexose oxidase (HOX)-dependent production of hydrogen peroxide (H2O2). We examined crude extracts from five different red algal species for their ability to prevent bacterial growth. The extract from one of these algae, Ptilophora subcostata, was particularly active and prevented the growth of gram-positive and -negative bacteria, which was completely inhibited by treatment with catalase. The extract did not affect the growth of either a yeast or a filamentous fungus. We partially purified from P. subcostata an enzyme involved in its antibacterial activity, which shared 50% homology with the HOX of red seaweed Chondrus crispus. In-gel carbohydrate oxidase assays revealed that P. subcostata extract had the ability to produce H2O2 in a hexose-dependent manner and this activity was highest in the presence of galactose. In addition, Bacillus subtilis growth was strongly suppressed near P. subcostata algal fronds on GYP agar plates. These results suggest that HOX plays a role in P. subcostata resistance to bacterial attack by mediating H2O2 production in the marine environment.

SUBMITTER: Ogasawara K

PROVIDER: S-EPMC4750953 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In humans, sulfite is generated endogenously by the metabolism of sulfur containing amino acids such as methionine and cysteine. Sulfite is also formed from exposure to sulfur dioxide, one of the major environmental pollutants. Sulfite is used as an antioxidant and preservative in dried fruits, vegetables, and beverages such as wine. Sulfite is also used as a stabilizer in many drugs. Sulfite toxicity has been associated with allergic reactions characterized by sulfite sensitivity, asthma, and anaphylactic shock. Sulfite is also toxic to neurons and cardiovascular cells. Recent studies suggest that the cytotoxicity of sulfite is mediated by free radicals; however, molecular mechanisms involved in sulfite toxicity are not fully understood. Cytochrome c (cyt c) is known to participate in mitochondrial respiration and has antioxidant and peroxidase activities. Studies were performed to understand the related mechanism of oxidation of sulfite and radical generation by ferric cytochrome c (Fe3+ cyt c) in the absence and presence of H2O2. Electron paramagnetic resonance (EPR) spin trapping studies using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) were performed with sulfite, Fe3+ cyt c, and H2O2. An EPR spectrum corresponding to the sulfite radical adducts of DMPO (DMPO-SO3-) was obtained. The amount of DMPO-SO3- formed from the oxidation of sulfite by the Fe3+ cyt c increased with sulfite concentration. In addition, the amount of DMPO-SO3- formed by the peroxidase activity of Fe3+ cyt c also increased with sulfite and H2O2 concentration. From these results, we propose a mechanism in which the Fe3+ cyt c and its peroxidase activity oxidizes sulfite to sulfite radical. Our results suggest that Fe3+ cyt c could have a novel role in the deleterious effects of sulfite in biological systems due to increased production of sulfite radical. It also shows that the increased production of sulfite radical may be responsible for neurotoxicity and some of the injuries which occur to humans born with molybdenum cofactor and sulfite oxidase deficiencies.

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Hexose Oxidase-Mediated Hydrogen Peroxide as a Mechanism for the Antibacterial Activity in the Red Seaweed Ptilophora subcostata.

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