Lipid metabolism in microsomal fraction from photosynthetic tissue. Effects of catalase and hydrogen peroxide on oleate desaturation.
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ABSTRACT:
SUBMITTER: Murphy DJ
PROVIDER: S-EPMC1152115 | biostudies-other | 1983 Jul
REPOSITORIES: biostudies-other
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Project description:Environmental stimuli such as UV, pathogen attack, and gravity can induce rapid changes in hydrogen peroxide (H(2)O(2)) levels, leading to a variety of physiological responses in plants. Catalase, which is involved in the degradation of H(2)O(2) into water and oxygen, is the major H(2)O(2)-scavenging enzyme in all aerobic organisms. A close interaction exists between intracellular H(2)O(2) and cytosolic calcium in response to biotic and abiotic stresses. Studies indicate that an increase in cytosolic calcium boosts the generation of H(2)O(2). Here we report that calmodulin (CaM), a ubiquitous calcium-binding protein, binds to and activates some plant catalases in the presence of calcium, but calcium/CaM does not have any effect on bacterial, fungal, bovine, or human catalase. These results document that calcium/CaM can down-regulate H(2)O(2) levels in plants by stimulating the catalytic activity of plant catalase. Furthermore, these results provide evidence indicating that calcium has dual functions in regulating H(2)O(2) homeostasis, which in turn influences redox signaling in response to environmental signals in plants.
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Project description:The role of the two known catalases in Pseudomonas aeruginosa in protecting planktonic and biofilm cells against hydrogen peroxide (H(2)O(2)) was investigated. Planktonic cultures and biofilms formed by the wild-type strain PAO1 and the katA and katB catalase mutants were compared for their susceptibility to H(2)O(2). Over the course of 1 h, wild-type cell viability decreased steadily in planktonic cells exposed to a single dose of 50 mM H(2)O(2), whereas biofilm cell viability remained at approximately 90% when cells were exposed to a flowing stream of 50 mM H(2)O(2). The katB mutant, lacking the H(2)O(2)-inducible catalase KatB, was similar to the wild-type strain with respect to H(2)O(2) resistance. The katA mutant possessed undetectable catalase activity. Planktonic katA mutant cultures were hypersusceptible to a single dose of 50 mM H(2)O(2), while biofilms displayed a 10-fold reduction in the number of culturable cells after a 1-h exposure to 50 mM H(2)O(2). Catalase activity assays, activity stains in nondenaturing polyacrylamide gels, and lacZ reporter genes were used to characterize the oxidative stress responses of planktonic cultures and biofilms. Enzyme assays and catalase activity bands in nondenaturing polyacrylamide gels showed significant KatB catalase induction occurred in biofilms after a 20-min exposure to H(2)O(2), suggesting that biofilms were capable of a rapid adaptive response to the oxidant. Reporter gene data obtained with a katB::lacZ transcriptional reporter strain confirmed katB induction and that the increase in total cellular catalase activity was attributable to KatB. Biofilms upregulated the reporter in the constant presence of 50 mM H(2)O(2), while planktonic cells were overwhelmed by a single 50 mM dose and were unable to make detectable levels of beta-galactosidase. The results of this study demonstrated the following: the constitutively expressed KatA catalase is important for resistance of planktonic and biofilm P. aeruginosa to H(2)O(2), particularly at high H(2)O(2) concentrations; KatB is induced in both planktonic and biofilm cells in response to H(2)O(2) insult, but plays a relatively small role in biofilm resistance; and KatB is important to either planktonic cells or biofilm cells for acquired antioxidant resistance when initial levels of H(2)O(2) are sublethal.
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Project description:1. The mechanisms of catalase action advanced by Jones & Wynne-Jones (1962) and by Nicholls (1964) are compared in terms of their relative plausibilities and their utility for extension to accommodate more recent experimental information. 2. A revised formal mechanism is advanced that avoids the less satisfactory features of these mechanisms and attempts to account for the roles of catalase sub-units in both reversible and irreversible deactivation phenomena. 3. Theoretical studies of the redox chemistry of peroxides are used to provide the basis for a discussion of the mechanism of the redox act in catalatic action at the molecular level. It is suggested that an important feature of catalase action may be a mediation of the formation of a reactive intermediate by stereospecifically located acid-base functions in the active site. 4. A more detailed statement of this concept is attempted in terms of a hypothetical partial molecular model for the composition and stereochemistry of the active site of catalase. The utility of this model in describing the catalatic and peroxidatic actions of catalase is assessed.
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Project description:We have studied the influence of experimental hyperthyroidism in the rat on the synthesis of unsaturated fatty acids and on liver microsomal lipid fatty-acid composition. Tri-iodothyronine treatment (25 micrograms/100 g body weight) daily for 3 weeks caused no significant changes in delta 9 (stearate) desaturation but a 24% decrease in delta 6 (linoleate) desaturation. Much larger doses of tri-iodothyronine increased delta 9 desaturation. Liver microsomal fatty-acid composition in hyperthyroidism is altered with significantly increased proportions of stearate and arachidonate and decreased proportions of palmitate, palmitoleate, linoleate (C18:2) and eicosa-8,11,14-trienoate (C20:3). These changes, other than the decreases proportion of C20:3 fatty acid, which may be due to the diminished delta 6 desaturase activity, cannot be attributed to changes in fatty-acid desaturation. Most of these changes were also found to be due not simply to the decreased weight gain or the increased food intake of the hyperthyroid animals. Only the decreased C18:2 fatty-acid proportions could be mimicked by restricting food intake of control animals and none of the changes were prevented by restricting food intake of hyperthyroid animals. Thus most of the changes in microsomal lipid fatty-acid composition are likely to be due to a thyroid hormone effect on peripheral lipid mobilization or lipid degradation.
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Project description:We have studied the influence of experimental hypothyroidism in the rat on the synthesis of unsaturated fatty acids and on liver microsomal lipid fatty acid composition. Hypothyroid rats demonstrated an 80% decrease in delta 9 (stearate) desaturation and a 43% decrease in delta 6 (linoleate) desaturation. Liver microsomal fatty acid composition was altered in the hypothyroid animals with a significantly decreased proportion of arachidonate and increased proportions of linoleate, eicosa-8,11,14-trienoate, eicosapentaenoate and docosahexaenoate. The bulk of these changes occurred in both of the two major phospholipid components, phosphatidylcholine and phosphatidylethanolamine. All of the changes were corrected by treatment of the hypothyroid rat with 25 micrograms of tri-iodothyronine/100 g body wt. twice daily. The diminished delta 9 desaturation did not lead to any changes in fatty acid composition. The increased linoleate and decreased arachidonate levels may be due to the diminished delta 6 desaturase activity, the rate-controlling step in the conversion of linoleate into arachidonate. The increases in the proportions of the other polyunsaturated fatty acid components cannot be explained by changes in the synthesis of unsaturated fatty acids, but are probably due to diminished utilization of these fatty acids.
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