PubMed · 11941332
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Abraham M Blechman. 2002. Functional magnetic system.. https://doi.org/10.1067/mod.2002.123337
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Cobalt influences the methanol metabolism of Desulfofundulus kuznetsovii TPOSR, specifically by modulating the activity of one of its alcohol dehydrogenases (ADH), Adh1. However, the effects of cobalt on the broader proteome of strain TPOSR, as well as the utilization of alcohols besides methanol, remain unexplored. Here, proteomic analyses of strain TPOSR grown with and without cobalt on different alcohol substrates show that cobalt starvation impacts multiple cellular processes, including cobalamin biosynthesis, iron-sulphur cluster assembly and, most prominently, energy metabolism as indicated by altered abundances of hydrogenases and NAD(P)-dependent oxidoreductases. Despite the presence of six ADH-encoding genes in the genome, Adh1 is the dominant ADH during growth not only on methanol but also on several primary alcohols and diols (ethanol, 1-propanol, 1,2-propanediol, 1,3-propanediol, butanol, pentanol and heptanol). Enzymatic assays with purified Adh1 confirm activity with these substrates, except 1,3-propanediol, and show no activity toward secondary alcohols (2-propanol and 2-butanol). Comparative proteomics analyses of other sulphate-reducing microorganisms (SRMs), namely Desulfofundulus australicum and Solidesulfovibrio carbinolicus, further indicate that methanol and ethanol oxidation in SRMs is mediated by a single ADH/AOR pair. Together, these findings highlight the central role of cobalt in alcohol metabolism in strain TPOSR and identify conserved ADH/AOR enzymes as promising candidates for biotechnological applications.
The electron transfer (ET) properties of a series of closely related cobalt porphyrins, [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]cobalt, CoF(28)TPP, [2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-tetraphenyl)porphyrinato]cobalt, CoF(8)TPP, 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]cobalt, CoF(20)TPP, and [5,10,15,20-tetraphenylporphyrinato]cobalt, CoTPP, were investigated by cyclic voltammetry, cyclic voltammetric digital simulation, in situ UV-vis and IR spectroelectrochemistry, kinetic ET studies, bulk electrolysis, (19)F NMR spectroscopy, X-ray crystallography, and molecular modeling. In benzonitrile containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF(6)) as supporting electrolyte, the ET rate constants for the Co(2+/3+) redox couples were found to be strongly substituent dependent; the heterogeneous ET rate constant (k(el)) varied by a factor of 10(4), and the ET self-exchange rate constants (k(ex)) varied over 7 orders of magnitude for the compounds studied. The remaining observed ring oxidation and metal and ring reduction events exhibited nearly identical k(el) values for all compounds. UV-vis and IR spectroelectrochemistry, bulk electrolysis, and (19)F NMR spectroscopic studies support attribution of different ET rates to widely varying inner sphere reorganization energies (lambda(i)) for these closely related compounds. Structural and semiempirical (PM3) studies indicate that the divergent kinetic behavior of CoTPP, CoF(8)TPP, CoF(20)TPP, and CoF(28)TPP first oxidations arises mainly from large nuclear reorganization energies primarily associated with core contraction and dilation. Taken together, these studies provide rational design principles for modulating ET rate constants in cobalt porphyrins over an even larger range and provide strategies for similar manipulation of ET rates in other porphyrin-based systems: substituents that lower C-C, C-N, and N-M vibrational frequencies or minimize porphyrin orbital overlap with the metal-centered orbital undergoing a change in electron population will increase k(ET). The heme ruffling apparent in electron transfer proteins such as cytochrome c is interpreted as nature's exploitation of this design strategy.
Treatment of fac(S)-[Rh(aet)3] (aet = 2-aminoethanethiolate) with aqueous HBF4 in air led to the protonation at coordinated thiolato groups to give a rhodium(III) dimer, [{Rh(aet)2(Haet)}{Rh(aet)(Haet)2}](BF4)3 ([1](BF4)3). On the other hand, similar treatment of fac(Se)-[Rh(aes)3] (aes = 2-aminoethaneselenolate) produced a dinuclear rhodium(III) complex, [Rh2(selenocystamine)3](BF4)6 ([2](BF4)6), because of the autoxidation of coordinated selenolato groups by air. The crystal structures of [1](BF4)3, DeltaDelta-[1](BF4)3, and [2](BF4)6 were determined by X-ray crystallography. In [1]3+ two RhIII octahedrons are connected through a strong triple thiol-thiolate S-H...S hydrogen bond, while two RhIII octahedrons are directly joined by a triple diselenide bond in [2]6+. The cyclic voltammetry indicated that in acidic media the RhIII center in fac(Se)-[Rh(aes)3] is more easily oxidized to RhIV than that in fac(S)-[Rh(aet)3], which is responsible for the formation of coordinated diselenide bonds.