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Inhibition of Saccharomyces cerevisiae phosphomannose isomerase by the NO-donor S-nitroso-acetyl-penicillamine
No full textPhosphomannose isomerase (PMI; EC. 5.3.1.8) is an essential metalloenzyme in the early steps of the protein glycosylation pathway in both prokaryotes and eukaryotes. The Cys150 residue (according to Candida albicans PMI numbering) is conserved in the active centre of mammalian and yeast PMI, but not in bacterial species where it is replaced by Asn. Here, the dose- and time-dependent inhibitory effect of the NO-donor S-nitroso-acetyl-penicillamine on the Saccharomyces cerevisiae PMI catalytic activity is reported. The analysis of the X-ray crystal structure of C. albicans PMI and of the molecular model of S. cerevisiae PMI provides a rationale for the low reactivity of Cys150 towards alkylating and nitrosylating agents
Nitrosylation of rabbit ferrous heme-hemopexin
No full textHemopexin (HPX) serves as a trap for toxic plasma heme, ensuring its complete clearance by transportation to the liver. Moreover, HPX-heme has been postulated to play a key role in the homeostasis of nitric oxide (NO). Here, the thermodynamics for NO binding to rabbit ferrous HPX-heme as well as the EPR and optical absorption spectroscopic properties of rabbit ferrous nitrosylated HPX-heme (HPX-heme-NO) are reported. The value of the dissociation equilibrium constant for NO binding to rabbit ferrous HPX-heme (i.e., H) is (1.4±0.2)×10–7 M, at pH 7.0 and 10.0 °C; the value of H is unaffected by sodium chloride. At pH 7.0, rabbit ferrous HPX-heme-NO is a six-coordinate heme-iron species, characterized by an X-band EPR spectrum with an axial geometry and by =146 mM–1 cm–1 at 419 nm. At pH 4.0, rabbit ferrous HPX-heme-NO is a five-coordinate heme-iron species, characterized by an X-band EPR spectrum with three-line splitting centered at 334 mT and by =74 mM–1 cm–1 at 387 nm. The pKa value of the reversible pH-induced six- to five-coordinate spectroscopic transition is 4.8±0.1 in the absence of sodium chloride and 4.3±0.1 in the presence of 1.5×10–1 M sodium chloride. This result is in agreement with the effect of sodium chloride on rabbit HPX-heme stability. The present data have been analyzed in parallel with those of a related heme model compound and heme-protein systems
Inhibition of Saccharomyces cerevisiae phosphomannose isomerase by the NO-donor S-nitroso-acetyl-penicillamine
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The heme-iron geometry of ferrous nitrosylated heme-serum lipoproteins, hemopexin, and albumin: a comparative EPR study
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The heme-iron geometry of ferrous nitrosylated heme-serum lipoproteins, hemopexin, and albumin: a comparative EPR study
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