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RISS 인기검색어
- 검색키워드
- 저자 : Paul A. Lindahl (검색결과 3 건)
- 무료
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Park, Jinkyu,McCormick, Sean P.,Cockrell, Allison L.,Chakrabarti, Mrinmoy,Lindahl, Paul A. American Chemical Society 2014 Biochemistry Vol.53 No.24
<P/><P>The majority of Fe in Fe-replete yeast cells is located in vacuoles. These acidic organelles store Fe for use under Fe-deficient conditions and they sequester it from other parts of the cell to avoid Fe-associated toxicity. Vacuolar Fe is predominantly in the form of one or more magnetically isolated nonheme high-spin (NHHS) Fe<SUP>III</SUP> complexes with polyphosphate-related ligands. Some Fe<SUP>III</SUP> oxyhydroxide nanoparticles may also be present in these organelles, perhaps in equilibrium with the NHHS Fe<SUP>III</SUP>. Little is known regarding the chemical properties of vacuolar Fe. When grown on adenine-deficient medium (A↓), ADE2Δ strains of yeast such as W303 produce a toxic intermediate in the adenine biosynthetic pathway. This intermediate is conjugated with glutathione and shuttled into the vacuole for detoxification. The iron content of A↓ W303 cells was determined by Mössbauer and EPR spectroscopies. As they transitioned from exponential growth to stationary state, A↓ cells (supplemented with 40 μM Fe<SUP>III</SUP> citrate) accumulated two major NHHS Fe<SUP>II</SUP> species as the vacuolar NHHS Fe<SUP>III</SUP> species declined. This is evidence that vacuoles in A↓ cells are more reducing than those in adenine-sufficient cells. A↓ cells suffered less oxidative stress despite the abundance of NHHS Fe<SUP>II</SUP> complexes; such species typically promote Fenton chemistry. Most Fe in cells grown for 5 days with extra yeast-nitrogen-base, amino acids and bases in minimal medium was HS Fe<SUP>III</SUP> with insignificant amounts of nanoparticles. The vacuoles of these cells might be more acidic than normal and can accommodate high concentrations of HS Fe<SUP>III</SUP> species. Glucose levels and rapamycin (affecting the TOR system) affected cellular Fe content. This study illustrates the sensitivity of cellular Fe to changes in metabolism, redox state and pH. Such effects broaden our understanding of how Fe and overall cellular metabolism are integrated.</P>
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EPR Studies of the Active Sites of Carbon Monoxide Dehydrogenase from Clostridium thermoaceticum
Shin, Woonsup,Lindahl, Paul A. 한국분석과학회 1995 분석과학 Vol.8 No.4
The active sites of the nickel and iron-containing enzyme, carbon monoxide dehydrogenase (CODH) from clostridium thermoaceticum were investigated using Electron Paramagnetic Resonance (EPR) technique. CODH exhibits several spectral features called NiFeC, $g_{ave}=1.82$, $g_{ave}=1.86$. FCII signals which are originated from different clusters in this enzyme. CODH is know to catalyze two different kinds of reactions - acetyl-CoA synthesis and CO oxidation. The acetyl-CoA synthesis activity can be followed by monitoring CO/acetyl-CoA exchange. The addition of 1,10-phenanthroline (phen) to CODH selectively destroyed the CO/acetyl-CoA exchange activity and eliminated the NiFeC signal completely. CO oxidation activity and other EPR signals were unaffected. Such behavior demonstrates that CODH has two distinct active sites and that the NiFe complex is only responsible for the CO/acctyl-CoA exchange activity. Phen caused the removal of only 30% of Ni in the NiFe complex ($0.3Ni/{\alpha}{\beta}$) as shown by the quantitative metal analysis. The phen-treated CODH could be reactivated fully by incubation In $Ni^{2+}$ solution. Radioactive $^{63}Ni^{2+}$ was used to quantitate the amount of the $Ni^{2+}$ incorporated into phen-treated enzyme and showed that the amount was the same as the removed by the phen treatment. i.e. $0.3Ni/{\alpha}{\beta}$. This indicates that only 30% of NiFe complexes are labile and responsible for the CO/acctyl-CoA exchange activity, the other 70% are non-labile and have no exchange activity. This is the first clear evidence that the NiFe complex is heterogencous and labile and non-labile Ni sites arc interacting differently with substrates and chelating agents like phen.
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