• Journal of Microbiology and Biotechnology
• /
• v.30 no.8
• /
• pp.1261-1271
• /
• 2020

Cytochrome c_L (Cytc_L) is an essential protein in the process of methanol oxidation in methylotrophs. It receives an electron from the pyrroloquinoline quinone (PQQ) cofactor of methanol dehydrogenase (MDH) to produce formaldehyde. The direct electron transfer mechanism between Cytc_L and MDH remains unknown due to the lack of structural information. To help gain a better understanding of the mechanism, we determined the first crystal structure of heme c containing Cytc_L from the aquatic methylotrophic bacterium Methylophaga aminisulfidivorans MP^T at 2.13 Å resolution. The crystal structure of Ma-Cytc_L revealed its unique features compared to those of the terrestrial homologues. Apart from Fe in heme, three additional metal ion binding sites for Na⁺, Ca⁺, and Fe²⁺ were found, wherein the ions mostly formed coordination bonds with the amino acid residues on the loop (G93-Y111) that interacts with heme. Therefore, these ions seemed to enhance the stability of heme insertion by increasing the loop's steadiness. The basic N-terminal end, together with helix α4 and loop (G126 to Y136), contributed positive charge to the region. In contrast, the acidic C-terminal end provided a negatively charged surface, yielding several electrostatic contact points with partner proteins for electron transfer. These exceptional features of Ma-Cytc_L, along with the structural information of MDH, led us to hypothesize the need for an adapter protein bridging MDH to Cytc_L within appropriate proximity for electron transfer. With this knowledge in mind, the methanol oxidation complex reconstitution in vitro could be utilized to produce metabolic intermediates at the industry level.

• Journal of Microbiology and Biotechnology
• /
• v.12 no.5
• /
• pp.819-825
• /
• 2002

Methanol dehydrogenase (MDH) is a key enzyme in the process of methanol oxidation in methylotrophic bacteria. However, information on MDH genes from genus Methylobacillus is limited. In this study, a 6.5-kb HindIII DNA fragment of Methylobacillus sp. SK-5 chromosomal DNA was isolated from the genomic library of the strain by using a degenerate oligonucleotide probe that was designed based on JV-terminal amino acid sequence of the MDH $\alpha$ subunit purified from the strain. Molecular analysis of the fragment revealed four tightly clustered genes (mxaFJGI) involved in the methanol oxidation. The first and fourth genes were very similar to mxaF (77% identity for nucleotides an 78% identity for amino acids) and mxaF (67% Identity for nucleotides and 68% Identity for amino acids) genes, respectively, from Methylovorus sp. SSI. Genes mxaF and mxaI encode $\alpha$ and $\beta$ subunits of MDH, respectively. The two subunits were identified from purified MDH from Methylobacillus sp. SK-5. A dendrogram constructed by comparison of amino acid sequences of MDH u subunits suggests that MxaF from Methylobacillus sp. SK-5 belongs to a subfamily cluster of MDH u subunits from $\beta$-subgroup Proteobacteria. The subfamily cluster is separated from the other subfamily that consists of $\beta$- and $\gamma$-subgroup Proteobacteria. This study provided information on mn genes from a methylotrophic bacterium in $\beta$-subgroup Proteobacteria, which would aid to better develop a gene probe to detect one-carbon metabolizing bacteria.

• Korean Journal of Microbiology
• /
• v.46 no.3
• /
• pp.286-290
• /
• 2010

C-1 compounds are observed in anaerobic sediment of high salt environments. Thus, surface sediments and waters from these environments are therefore potential habitats for aerobic methylotrophic microorganisms. The soil samples collected from saltern and tidal flat as inoculums and methanol as carbon and energy source was supplied. After subculture depending on the salt concentration, methanol oxidizing bacteria growth condition investigated, the results of methanol oxidizing bacteria can grow in salt conditions, and the maximum concentration was 20%. Analysis based on denaturing gradient gel electrophoresis of 16S rRNA genes indicates that Methelyophaga-like bacteria were dominants of methylotrophs in the enrichment culture. Quantitative PCR showed that archaeal cells were about 1-10% of bacterial cells. Additionally archaea were assumed not to be involved in methanol oxidation since bacterial antibiotics completely blocked the methanol oxidation. Our results suggest that Methelyophaga-like bacteria could be involved in C-1 compounds oxidation in hypersaline environments although those activities are sensitive to salinity above 20%.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.06a
• /
• pp.369-372
• /
• 2009

In the present study, the effect of chemical treatment on graphite nanofibers (GNFs) supports with various concentrated nitric acids was investigated for methanol oxidation. To optimize the electrocatalytic activity, PtRu catalysts were deposited on GNF supports by impregnation method. The surface and structural properties of the GNF supports were characterized by X-ray photoelectron spectroscopy (XPS), element analyzer (EA), and X-ray diffraction (XRD). The morphology of the catalysts was observed by means of transmission electron microscopy (TEM). The electrocatalytic activity of PtRu/GNF catalysts was investigated by cyclic voltammetry measurement. As a result, the oxygen functional groups were introduced on the GNF supports and were gradually increased with increasing of concentrated nitric acid, causing the smaller particle size and higher loading level. And the electrocatalytic activity of the catalysts for methanol oxidation was gradually improved. Consequently, it was found that chemical treatments could influence on surface properties of the carbon supports, resulting in enhancing the electrocatalytic activity of the catalysts for DMFCs.

• Journal of Electrochemical Science and Technology
• /
• v.10 no.3
• /
• pp.284-293
• /
• 2019

Herein, we report an electrode surface with a hierarchical assembly of wild-type M13 virus nanofibers (M13) to nucleate the AuPt alloy nanostructures by electrodeposition. M13 was pulled on the electrode surface to produce a virus film, and then a layer of sol-gel matrix (SSG) was wrapped over the surface to protect the film, thereby a bio-template was constructed. Blending of metal binding domains of M13 and amine groups of the SSG of the bio-template were effectively nucleate and directed the growth of nanostructures (NSs) such as Au, Pt and AuPt alloy onto the modified electrode surface by electrodeposition. An electrocatalytic activity of the modified electrode toward methanol oxidation in alkaline medium was investigated and found an enhanced mass activity ($534mA/mg_{Pt}$) relative to its controlled experiments. This bio-templated growth of NSs with precise composition could expedite the intention of new alloy materials with tuneable properties and will have efficacy in green energy, catalytic, and energy storage applications.

• Carbon letters
• /
• v.14 no.2
• /
• pp.117-120
• /
• 2013

In this study, an electro-catalyst of Pt nanoparticles supported by polypyrrole-functionalized graphene (Pt/PPy-reduced graphene oxide [RGO]) is reported. The Pt nanoparticles are deposited on the PPy-RGO composite by chemical reduction of H2PtCl6 using NaBH4. The presence of graphene (RGO) caused higher activity. This might have been due to increased electro-chemically accessible surface areas, increased electronic conductivity, and easier charge-transfer at polymer-electrolyte interfaces, allowing higher dispersion and utilization of the deposited Pt nano-particles. Microstructure, morphology and crystallinity of the synthesized materials were investigated using X-ray diffraction and transmission electron microscopy. The results showed successful deposition of Pt nano-particles, with crystallite size of about 2.7 nm, on the PPy-RGO support film. Catalytic activity for methanol electro-oxidation in fuel cells was investigated using cyclic voltammetry. The fundamental electrochemical test results indicated that the electro-catalytic activity, for methanol oxidation, of the Pt/PPy-RGO combination was much better than for commercial catalyst.

• Journal of Food Hygiene and Safety
• /
• v.14 no.2
• /
• pp.153-159
• /
• 1999

This study was undertaken to evaluate antioxidative activities of substances isolated from marine resources against human low density lipoprotein (LDL). Methanol-water extract(80 : 20, v/v) of Sargassum ringgoldianum had the highest antioxidant activity and the active substance was purified by silica gel column chromatography by eluting chlorform : methanol mixture (80 : 20 v/v). The active fraction was seperated to several spots on the TLC in chlorofrom : methanol (10 : 1, v/v) mixture. Antioxidative activity of band 4 of fraction 2 on TLC was highest than that of $\alpha$-tocopherol against human LDL oxidation by the method of thiobarbituric acid reactive substance (TBARS). The band 4 of fraction 2 inhibited the copper mediated oxidation of human LDL with almost completely at 1 or 2 mg/ml.

• Journal of the Korean Chemical Society
• /
• v.38 no.4
• /
• pp.302-308
• /
• 1994

Homogeneous catalytic oxidation of hydrazobenzene was investigated by employing pentadentate Schiff base complexes such as [Co(II)(Sal-DPT)(H$_2$O)] and [Co(II)(Sal-DET)(H$_2$O)] in oxygen-saturated methanol solvent. The oxidation product of hydrazobenzene(H$_2$AB) was trans-azobenzene(trans-AB). The rate constants of oxidation reaction measured by UV-visible spectrophotometry were observed as $6.06{\times}10^{-3}sec^{-1}$ for [Co(II)(Sal-DPT)(H$_2$O)] and $2.50{\times}10^{-3}sec^{-1}$ for [Co(II)(Sal-DET)(H$_2$O)]. The mechanism of oxidation reaction for H$_2$AB by homogeneous activated catalysts has been proposed as following. H$_2$AB + Co(II)(L)(H$_2$O) + O$_2$ $\rightleftharpoons^K_{MeOH}Co(III)(L)O_2{\cdot}H_2AB + H_2O\longrightarrow^{k}Co(II)(L) + trans-AB + H_2O_2$ (L: Sal-DPT and Sal-DET)

• Journal of Electrochemical Science and Technology
• /
• v.1 no.1
• /
• pp.19-24
• /
• 2010

Alloying degree is an important structural factor of PtRu catalysts for direct methanol fuel cells (DMFC). In this work, carbon supported PtRu catalysts were synthesized by reduction method using anhydrous ethanol as a solvent and $NaBH_4$ as a reducing agent. Using anhydrous ethanol as a solvent resulted in high alloying degree and good dispersion. The morphological structure and crystallanity of synthesized catalysts were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM). CO stripping and methanol oxidation reaction were measured. Due to high alloying degree catalyst prepared in anhydrous ethanol, exhibited low onset potential for methanol oxidation and negative peak shift of CO oxidation than commercial sample. Consequently, samples, applying ethanol as a solvent, exhibited not only enhanced CO oxidation, but also increased methanol oxidation reaction (MOR) activity compared with commercial PtRu/C (40 wt%, E-tek) and 40 wt% PtRu/C prepared in water solution.

• 한국생물공학회:학술대회논문집
• /
• 2003.04a
• /
• pp.116-120
• /
• 2003

Type strain, Methylosinus trichosporium OB3b, was used to convert methane to methanol. To prevent further oxidation of methanol, NaCl and EDTA were used as inhibitors of methanol dehydrogenase. The reaction temperature was $25^{\circ}C$, and the concentrations of cell and sodium formate added to the reaction mixture were 0.6 mg dry cell wt/ml and 20 mM, respectively. During 12hr reaction, 8 mM methanol was accumulated in the reaction mixture. In this reaction $K_m$ and $V_{max}$ values were found to be 532.6 mM and 1.749 mmol/hr, respectively, and the conversion rate was approximately 37%. To increase the concentration of methanol in the medium, a repeated batch reaction was carried out. In this process, methane was injected every eight hours, and the produced methanol concentration was 18 mM.