5,6,7,8-Tetrahydromethanopterin-dependent enzymes involved in methanogenesis

Abstract In the process of methanogenesis, 5,6,7,8-tetrahydromethanopterin (H₄MPT) is the carrier of the C₁ unit at the formyl through methyl state of reduction. By the transfer of a formyl group from formylmethanofuran, 5-formyl- and 10-formyl-H₄MPT are formed in hydrogenotrophic and methylotrophic organisms, respectively. Cyclohydrolysis of the 5- and 10-formyl derivatives then yields 5,10-methenyl-H₄MPT, which is reduced in two subsequent coenzyme F₄₂₀-dependent reactions to 5-methyl-H₄MPT. Following the transfer of the methyl group to coenzyme M, the substrate of the terminal step in methanogenesis, methylcoenzyme M, is produced. In this paper properties of the enzymes catalyzing the individual H₄MPT-dependent reactions are discussed.     

Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

Interconversion of F430 derivatives of methanogenic bacteria

F₄₃₀ is the prosthetic group of the methylcoenzyme M reductase of methanogenic bacteria. The compound isolated from Methanosarcina barkeri appears to be identical to the one obtained from the only distinctly related Methanobacterium thermoautotrophicum. F₄₃₀ is thermolabile and in the presence of acetonitrile or C10 _in4 ^sup- two epimerization products are obtained upon heating; in the absence of these compounds F₄₃₀ is oxidized to 12, 13-didehydro-F₄₃₀. The latter is stereoselectively reduced under H₂ atmosphere to F₄₃₀ by cell-free extracts of M. barkeri or M. thermoautotrophicum. H₂ may be replaced by the reduced methanogenic electron carrier coenzyme F₄₂₀.Abbreviations CH₃S-CoM methylcoenzyme M, 2-methylthioethanesulfonic acid - HS-CoM coenzyme M, 2-mercaptoethanesulfonic acid - F₄₃₀ Ni(II) tetrahydro-(12, 13)-corphin with a uroporphinoid (III) ligand skeleton - 13-epi-F₄₃₀ and 12,13-di-epi-F₄₃₀ the 12, 13- and 12, 13-derivatives of F₄₃₀ - 12, 13-didehydro-F₄₃₀ F₄₃₀ oxidized at C-12 and C-13 - coenzyme F₄₂₀ 7,8-didemethyl-8-hydroxy-5-deazaflavin derivative - coenzyme F₄₂₀H₂ reduced coenzyme F₄₂₀ - MV⁺ methylviologen semiquinone - HPLC high-performance liquid chromatography     

Structural characterization of tatiopterin, a novel pterin isolated from Methanogenium tationis

Cofactor extracts of Methanogenium tationis were screened for the presence of pterin-derivatives. Methanopterin, sarcinapterin and 7-methylpterin were absent, while 2-amino-4-hydroxy-pteridine and another blue fluorescent compound with a pterin spectrum were detected. The latter pterin was purified by ion exchange and reversed-phase column chromatography. The structure of this compound was elucidated by combining spectrophotometry, amino acid analysis and 1H-NMR spectroscopy. The pterin, which we named tatiopterin, was identified as an aspartyl derivative of sarcinapterin with a 7-proton instead of a 7-methyl group in the pterin moiety. The IUPAC name is: N-[-1'-(2'-amino-4'-hydroxy-7'-proton-6'-pteridinyl)ethyl]-4- [2',3',4',5'-tetrahydroxypent-1'-yl(5'----1')O-alpha- ribofuranosyl-5'-phosphoric acid]aniline, in which the phosphate group is esterified with alpha-hydroxyglutarylglutamylaspartic acid.     

Interactions between aluminium,magnesium and calcium with different monocotyledonous and dicotyledonous plant species

Growth inhibition of plants suffering from Al toxicity is generally accompanied by impaired root development which can be quantitatively described by reduced specific root length (m g^-1 dry root). In addition, the uptake of nutrients such as Mg and Ca is inhibited. Increased supply of either Mg or Ca can significantly diminish the negative effect of Al on root development and improve the Mg or Ca nutrition of the plants. The positive effect of Ca is well established but the effect of Mg has been observed in only a few plan species. Therefore, the effects of increasing Mg and Ca supply on Al toxicity in plants of seven monocots and eight dicots have been now examined in nutrient solution experiments. In general, Mg appears to be more effective than Ca in alleviating Al toxicity with the monocots, whereas the reverse is true for the dicots. Increased concentrations of Mg and Ca in solution seem to protect the plants against Al toxicity by improving the Mg or Ca nutrition and by alleviating the toxic effect of Al on root development.     

Involvement of an activation protein in the methanol:2-mercaptoethanesulfonic acid methyltransferase reaction in Methanosarcina barkeri.

Methanol:5-hydroxybenzimidazolylcobamide methyltransferase (MT1) is the first of two enzymes required for transfer of the methyl group of methanol to 2-mercaptoethanesulfonic acid in Methanosarcina barkeri. MT1 binds the methyl group of methanol to its corrinoid prosthetic group only when the central cobalt atom of the corrinoid is present in the highly reduced Co(I) state. However, upon manipulation of MT1 and even during catalysis, the enzyme becomes inactivated as the result of Co(I) oxidation. Reactivation requires H2, hydrogenase, and ATP. Ferredoxin stimulated the apparent reaction rate of methyl group transfer. Here we report that one more protein fraction was found essential for the overall reaction and, more specifically, for formation of the methylated MT1 intermediate. The more of the protein that was present, the shorter the delay of the start of methyl group transfer. The maximum velocity of methyl transfer was not substantially affected by these varying amounts of protein. This demonstrated that the protein was involved in the activation of MT1. Therefore, it was called methyltransferase activation protein.     

Transpiration and drought resistance of Douglas-fir seedlings exposed to excess ammonium

 In a pot trial growth and transpiration of 3-year-old Douglas-fir seedlings on an acid, sandy soil was examined at a deficient (30 kg N ha^{–  1} year^{–  1}) and an excessive level (120 kg N ha^{–  1} year^{–  1}) of NH₄ application. Dissolved ammonium sulphate was applied to the pots weekly for two growing seasons. In half of the pots a complete set of other nutrients was applied in optimal proportions to the applied nitrogen. Water supply was optimal and transpiration was recorded. At the end of the second treatment season irrigation was stopped for 2 weeks during dry and sunny weather. Both high application of NH₄ and additional nutrients increased shoot growth and transpiration demand in the first treatment year. The root system was smaller at higher N level and this reduced water uptake accordingly. In the second year the combination of high NH₄ ⁺ and additional nutrients affected root functioning predominantly due to salinity effects and this seriously decreased water uptake capacity and shoot water potentials, finally resulting in tree death. Without addition of other nutrients the high NH₄ ⁺ application resulted in a high degree of soil acidification, which damaged the roots, that showed a decrease in water uptake capacity. At the low NH₄ supply level soil acidification was lower, and root functioning was not affected, and the trees recovered quickly from the imposed drought. Higher needle K and P status depressed transpiration rates at the low NH₄ application rate. Received: 9 January 1995 / Accepted: 18 September 1995     

Methanogenesis: surprising molecules,microorganisms and ecosystems

Methanogenesis involves a novel set of coenzymes as one-carbon and electron carriers. Consequently, metabolic processes of methanogens deviate from those present in non-methanogenic bacteria. Methanogenic bacteria can be classified on the basis of substrate utilization. Group I (24 species) grows at the expense of hydrogen plus CO₂ and/or formate and group II (7 species) uses methanol and/or acetate. Hydrogen-consuming methanogens are found as epi- or endosymbionts of anaerobic ciliates.     

Identification of 6-acetyl-7-methyl-7,8-dihydropterin as a degradation product of 5,10-methenyl-5,6,7,8-tetrahydromethanopterin

During purification procedures and upon aerobic heating with alkali a green-yellow degradation fluorescent product (GY) was formed from 5,10-methenyl-5,6,7,8-tetrahydromethanopterin, an intermediate in the reduction of CO₂ to methane [J. T. Keltjens, L. Daniels, H. G. Janssen, and G. D. Vogels (1983)Eur. J. Biochem.130, 545–552]. GY was suggested to be a 6-(1-oxo)-7,8-dihydropterin. On the basis of the spectral properties and the results of degradation studies, it was now shown that the structure of GY is 6-acetyl-7-methyl-7,8-dihydropterin. This structure was confirmed by synthesis of the compound and other reference substances.     

Presence of coenzyme M derivatives in the prosthetic group (coenzyme MF430) of methylcoenzyme M reductase from Methanobacterium thermoautotrophicum

2-Mercaptoethanesulfonic acid (coenzyme M), or a derivative of it, and a yellow chromophore, known as the nickel-containing tetrapyrrole factor F₄₃₀, occur in the prosthetic group of methylcoenzyme M reductase in an equimolar amount, and bound to each other; this enzyme catalyzes the final step of methane production. The prosthetic group, which is called coenzyme MF₄₃₀, was isolated from the purified enzyme and was extracted from cells. The presence of coenzyme M was confirmed by a bioassay using Methanobrevibacter ruminantium and by the use of chemical and physicochemical analyses.