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  • 1. Cebula, Marcus
    et al.
    Turan, Ilke Simsek
    Sjödin, Birgitta
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Thulasingam, Madhuranayaki
    Brock, Joseph
    Chmyrov, Volodymyr
    Widengren, Jerker
    Abe, Hiroshi
    Mannervik, Bengt
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Haeggström, Jesper Z.
    Rinaldo-Matthis, Agnes
    Akkaya, Engin U.
    Morgenstern, Ralf
    Catalytic Conversion of Lipophilic Substrates by Phase constrained Enzymes in the Aqueous or in the Membrane Phase2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 38316Article in journal (Refereed)
    Abstract [en]

    Both soluble and membrane-bound enzymes can catalyze the conversion of lipophilic substrates. The precise substrate access path, with regard to phase, has however, until now relied on conjecture from enzyme structural data only (certainly giving credible and valuable hypotheses). Alternative methods have been missing. To obtain the first experimental evidence directly determining the access paths (of lipophilic substrates) to phase constrained enzymes we here describe the application of a BODIPY-derived substrate (PS1). Using this tool, which is not accessible to cytosolic enzymes in the presence of detergent and, by contrast, not accessible to membrane embedded enzymes in the absence of detergent, we demonstrate that cytosolic and microsomal glutathione transferases (GSTs), both catalyzing the activation of PS1, do so only within their respective phases. This approach can serve as a guideline to experimentally validate substrate access paths, a fundamental property of phase restricted enzymes. Examples of other enzyme classes with members in both phases are xenobiotic-metabolizing sulphotransferases/UDP-glucuronosyl transferases or epoxide hydrolases. Since specific GSTs have been suggested to contribute to tumor drug resistance, PS1 can also be utilized as a tool to discriminate between phase constrained members of these enzymes by analyzing samples in the absence and presence of Triton X-100.

  • 2. Huenchuguala, Sandro
    et al.
    Sjödin, Birgitta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Mannervik, Bengt
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Segura-Aguilar, Juan
    Novel Alpha-Synuclein Oligomers Formed with the Aminochrome-Glutathione Conjugate Are Not Neurotoxic2019In: Neurotoxicity research, ISSN 1029-8428, E-ISSN 1476-3524, Vol. 35, no 2, p. 432-440Article in journal (Refereed)
    Abstract [en]

    Aminochrome induces neurotoxic alpha-synuclein oligomer formation relevant to the etiology of Parkinson's disease. Oxidative stress produces aminochrome from dopamine, but conjugation with glutathione catalyzed by glutathione transferase M2-2 significantly decreases aminochrome-induced toxicity and alpha-synuclein oligomer formation. Notably, in the presence of the aminochrome-glutathione conjugate, previously unknown species of alpha-synuclein oligomers are formed. These aminochrome-glutathione oligomers of alpha-synuclein differ from formerly characterized oligomers and (i) have high molecular weight, and are stable and SDS-resistant, as determined by the Western blot method, (ii) show positive NBT-quinone-protein staining, which indicates the formation of alpha-synuclein adducts containing aminochrome. Furthermore, aminochrome-glutathione alpha-synuclein oligomers (iii) have distinctive shape and size, as determined by transmission electron microscopy, and (iv) are not toxic in U373MG cells. In conclusion, glutathione conjugated with aminochrome induces a new type of alpha-synuclein oligomers of a different size and shape, which have no demonstrable toxicity.

  • 3.
    Mannervik, Bengt
    et al.
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Sjödin, Birgitta
    Stockholm University, Faculty of Science, Department of Neurochemistry.
    Blood-Brain Barrier-Penetrating 6-Halogenopurines Suitable as Pro-Probes for Positron Emission Tomography are Substrates for Human Glutathione Transferases2016In: Pharmaceutical Bioprocessing, ISSN 2048-9145, Vol. 4, no 2, p. 25-30Article in journal (Refereed)
    Abstract [en]

    6-Chloro- and 6-bromopurines can cross the blood-brain barrier and in situ give rise to substrates of multidrug resistance-associated proteins (MRPs). The electrophilic purines form glutathione conjugates in reactions catalyzed by intracellular glutathione transferases (GSTs), and the conjugates are subsequently exported from the cells by ATP-dependent membrane transporters. In rodent model systems it has been demonstrated that suitably radiolabeled 6-halogenopurines by this scheme are pro-probes useful in monitoring the functionality of MRPs in intact brains using positron emission tomography. Prior to applications in human subjects it is imperative to establish the purine pro-probes as effective substrates for human GSTs occurring in brain and other tissues. We have developed a spectrophotometric assay for the glutathione conjugation and determined specific activities with a range of human GSTs as well as some rat GSTs for comparison. The ubiquitous GST P1-1 showed the highest activities with the 6-halogenopurines, which bodes well for the application of pro-probes for human investigations.

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