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Query: UNIPROT:P04040 (Catalase)
 3,577 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Catalase (EC 1.11.1.6) isoforms CAT 2 through CAT 8 were purified from peroxisomes of sunflower (Helianthus annuus L.) cotyledons and photoinactivated in vitro. Action and absorbance spectra between 380 and 727 nm wavelength showed most prominent maxima at 405 nm suggesting an inactivation mediated by light absorption of heme groups. First order kinetics of inactivation were observed for CAT 6 through CAT 8 (isoform group B), which are composed of four 55-kDa subunits. Inactivation constants ki depended on photon fluence rates in the studied range between 8.3 and 660 microE m(-2) s(-1). The maximal value of ki was about 4.0 h(-1), corresponding to a half-life of about 10 min. Heme groups and 55-kDa apoprotein moieties of group B isoforms were degraded during irradiation, but both degradation processes occurred at rates lower than those of inactivation. Quantitative evaluations contradicted the view that photoinactivation was caused by destruction or dissociation of heme but suggested apoprotein damage leading to the loss of activity. Group A isoforms CAT 2 through CAT 5, containing both 55- and 59-kDa subunits, were less photosensitive than the isoforms of group B. In addition, irradiated group A isoforms reached a low plateau of residual activity, whereas group B isoforms were inactivated completely. The 59-kDa subunits in group A isoforms were much more resistant to photodegradation than the 55-kDa subunits of group B isoforms and also much more resistant than their own 55-kDa cosubunits. Results presented here are compared with catalase photoinactivation and turnover in vivo and discussed with respect to a physiological significance of catalase isoforms in plant peroxisomes.
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PMID:In vitro photoinactivation of catalase isoforms from cotyledons of sunflower (Helianthus annuus L.). 934 68

Cyanobacterium Synechococcus sp. PCC 7002 contains a single gene (glbN) coding for GlbN, a protein of the 2/2 hemoglobin lineage. The precise function of GlbN is not known, but comparison to similar 2/2 hemoglobins suggests that reversible dioxygen binding is not its main activity. In this report, the results of in vitro and in vivo experiments probing the role of GlbN are presented. Transcription profiling indicated that glbN is not strongly regulated under any of a large number of growth conditions and that the gene is probably constitutively expressed. High levels of nitrate, used as the sole source of nitrogen, and exposure to nitric oxide were tolerated better by the wild-type strain than a glbN null mutant, whereas overproduction of GlbN in the null mutant background restored the wild-type growth. The cellular contents of reactive oxygen/nitrogen species were elevated in the null mutant under all conditions and were highest under NO challenge or in the presence of high nitrate concentrations. GlbN overproduction attenuated these contents significantly under the latter conditions. The analysis of cell extracts revealed that the heme of GlbN was covalently bound to overproduced GlbN apoprotein in cells grown under microoxic conditions. A peroxidase assay showed that purified GlbN does not possess significant hydrogen peroxidase activity. It was concluded that GlbN protects cells from reactive nitrogen species that could be encountered naturally during growth on nitrate or under denitrifying conditions. The solution structure of covalently modified GlbN was determined and used to rationalize some of its chemical properties.
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PMID:Functional and structural characterization of the 2/2 hemoglobin from Synechococcus sp. PCC 7002. 2066 34