1.The alkyl tert-butyl ether intermediate 2-hydroxyisobutyrate is degraded via a novel cobalamin-dependent mutase pathway.
Rohwerder T1, Breuer U, Benndorf D, Lechner U, Müller RH. Appl Environ Microbiol. 2006 Jun;72(6):4128-35.
Fuel oxygenates such as methyl and ethyl tert-butyl ether (MTBE and ETBE, respectively) are degraded only by a limited number of bacterial strains. The aerobic pathway is generally thought to run via tert-butyl alcohol (TBA) and 2-hydroxyisobutyrate (2-HIBA), whereas further steps are unclear. We have now demonstrated for the newly isolated beta-proteobacterial strains L108 and L10, as well as for the closely related strain CIP I-2052, that 2-HIBA was degraded by a cobalamin-dependent enzymatic step. In these strains, growth on substrates containing the tert-butyl moiety, such as MTBE, TBA, and 2-HIBA, was strictly dependent on cobalt, which could be replaced by cobalamin. Tandem mass spectrometry identified a 2-HIBA-induced protein with high similarity to a peptide whose gene sequence was found in the finished genome of the MTBE-degrading strain Methylibium petroleiphilum PM1. Alignment analysis identified it as the small subunit of isobutyryl-coenzyme A (CoA) mutase (ICM; EC 5.
2.tert-Butyl hydroperoxide-induced radical production in rat liver mitochondria.
Kennedy CH1, Church DF, Winston GW, Pryor WA. Free Radic Biol Med. 1992;12(5):381-7.
When rat liver mitochondria are treated with tert-butyl hydroperoxide (TBHP) in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), electron paramagnetic resonance (EPR) signals are detected attributable to spin adducts resulting from the trapping of methyl, tert-butoxyl, and tert-butylperoxyl radicals. The addition of respiratory substrate results in a 3- to 7.5-fold increase in the signal intensity of the DMPO/methyl adduct, no change in the signal intensity of the DMPO/tert-butoxyl adduct, and complete loss of the DMPO/tert-butylperoxyl adduct signal. The magnitude of increase of methyl radical production in the presence of respiratory substrate is related to the respiratory control ratio (RCR) of the mitochondrial preparation. In the presence of antimycin A, which blocks electron flow between cytochromes b and c1, no stimulation of methyl radical production is detected with respiratory substrate. Stimulation of methyl radical production by the addition of respiratory substrate is detected in cytochrome c-depleted mitochondria.
3.NADH-linked substrate dependence of peroxide-induced respiratory inhibition and calcium efflux in isolated renal mitochondria.
Vlessis AA1. J Biol Chem. 1990 Jan 25;265(3):1448-53.
Peroxide-induced state 3 respiratory inhibition and Ca2+ efflux in isolated renal mitochondria exhibited a NADH-linked substrate dependence. ADP-stimulated respiratory rates in the presence of various concentrations of tert-butyl hydroperoxide (tBOOH, 0-1000 nmol/mg protein) were determined using glutamate, beta-hydroxybutyrate, or pyruvate as substrates. Pyruvate-driven respiration was most sensitive to inhibition (Ki approximately equal to 75 nmol of tBOOH/mg protein) followed by beta-hydroxybutyrate and glutamate (Ki approximately equal to 150 nmol of tBOOH/mg protein for each). Calcium (5-10 nmol/mg protein) potentiated tBOOH-induced respiratory inhibition using all three substrates. Mitochondrial Ca2+ efflux, induced by tBOOH, was most pronounced with pyruvate as substrate. Glutamate prevented Ca2+ efflux while the efflux rate with beta-hydroxybutyrate was intermediate between glutamate and pyruvate. The substrate-dependent pattern of tBOOH-induced NAD(P)H (NADH plus NADPH) and cytochrome b oxidation was similar to that seen for respiratory inhibition and Ca2+ efflux suggesting that NAD(P)H may be a common factor in both responses.
4.Synthesis of the building block 2-hydroxyisobutyrate from fructose and butyrate by Cupriavidus necator H16.
Przybylski D1, Rohwerder T, Harms H, Yaneva N, Müller RH. Appl Microbiol Biotechnol. 2013 Oct;97(20):8875-85. doi: 10.1007/s00253-013-5064-x. Epub 2013 Aug 15.
2-Hydroxyisobutyryl-coenzyme A mutase, originally discovered in the context of methyl tert-butyl ether degradation in Aquincola tertiaricarbonis L108, catalyzes the isomerization of 3-hydroxybutyryl-coenzyme A (3-HB-CoA) to 2-hydroxyisobutyryl-CoA. It thus constitutes the basis for a biotechnological route from practically any renewable carbon to 2-hydroxyisobutyrate (2-HIB) via the common metabolite 3-hydroxybutyrate. At first sight, recombinant Cupriavidus necator H16 expressing the mutase seems to be well suited for such a synthesis process, as a strong overflow metabolism via (R)-3-HB-CoA is easily induced in this bacterium possessing the poly-3-hydroxybutyrate metabolism. However, the recently established stereospecificity of the mutase, dominantly preferring the (S)-enantiomer of 3-HB-CoA, calls for a closer investigation of C. necator as potential 2-HIB production strain and raised the question about the strain's potential to yield 2-HIB from substrates directly providing (S)-3-HB-CoA.