甲烷单加氧酶的催化机理

研究了来源于Ｍｅｔｈｙｌｏｍｏｎａｓｓｐ．ＧＹＪ３菌的甲烷单加氧酶（ＭＭＯ）催化机理，结果表明，用还原剂处理基于酶可得么不同还原态的羟基化酶，其中全还原态的羟基化酶具有ＭＭＯ催化活性，还原酶和调节蛋白单独存在的均没有ＭＭＯ活性，确定了羟基化酶组分是ＭＭＯ的催化活性中心，用紫外光谱法证实了ＮＡＤＨ和还原酶之间的相互作用，即还原酶接受ＮＡＤＨ的电子，使氧化态的ＦＡＤ转化为还原态的ＦＡＤ，ＭＭＯ的电子传     

Citric acid production with alginate bead entrappedAspergillus niger ATCC 9142

Aspergillus niger ATCC 9142 mycelium was entrapped in calcium alginate beads and employed in an air-lift completely stirred reactor for continuous production of citric acid. Maximum yield obtained from 10% (w/v) sucrose was 12 g dm^-3 with about 40% fermentation efficiency. Maximum rate of production 70 mg g^-1 h^-1 was about five times that obtained in classical batch fermentation.     

Chemical composition of essential oils from different parts of Protium heptaphyllum (Aubl.) Marchand and their in vitro antibacterial activity

Abstract

In Brazilian folk medicine, Protium heptaphyllum is used to treat inflammatory conditions and to hasten wound repair. This paper aims to investigate the chemical composition and the in vitro antibacterial effects of the essential oils (EOs) obtained from P. heptaphyllum leaves and ripe and unripe fruits against a representative panel of oral pathogens. The GC-FID and GC-MS analysis revealed that the major components determined in P. heptaphyllum essential oils were myrcene (59.0%), β-elemene (17.2%), limonene (12.9%), spathulenol (12.6%), α-cubebene (11.6%), germacrene D (10.6%), trans-nerolidol (9.8%), and α-cadinol (8.8%). The essential oils of the ripe and unripe fruits showed the strongest antibacterial activity against the anaerobic bacteria Prevotella nigrescens (MIC?=?50?µg/mL). The leaf essential oil displayed very promising activity against Streptococcus mutans (MIC?=?50?µg/mL) and Streptococcus mitis (MIC?=?62.5?µg/mL). The antibacterial activity of EOs against oral pathogens is also described for the first time.

     

Purification and characterization of two xylanases from alkalophilic and thermophilic Bacillus licheniformis 77-2

The alkalophilic bacteria Bacillus licheniformis 77-2 produces significant quantities of thermostable cellulase-free xylanases. The crude xylanase was purified to apparent homogeneity by gel filtration (G-75) and ionic exchange chromatography (carboxymethyl sephadex, Q sepharose, and Mono Q), resulting in the isolation of two xylanases. The molecular masses of the enzymes were estimated to be 17 kDa (X-I) and 40 kDa (X-II), as determined by SDS-PAGE. The K _m and V _max values were 1.8 mg/mL and 7.05 U/mg protein (X-I), and 1.05 mg/mL and 9.1 U/mg protein (X-II). The xylanases demonstrated optimum activity at pH 7.0 and 8.0–10.0 for xylanase X-I and X-II, respectively, and, retained more than 75% of hydrolytic activity up to pH 11.0. The purified enzymes were most active at 70 and 75°C for X-I and X-II, respectively, and, retained more than 90% of hydrolytic activity after 1 h of heating at 50°C and 60°C for X-I and X-II, respectively. The predominant products of xylan hydrolysates indicated that these enzymes were endoxylanases.     

Thermal quenching of fluorescence of freshwater, planktonic bacteria

This study aims to determine the thermal quenching properties of pure bacterial cultures as a means of aiding the development of fluorescence measurement in natural waters. The bacterium Pseudomonas aeruginosa was isolated from the urban River Tame, Birmingham, UK, and planktonic bacteria were grown in sterile, sealed glass jars, in 100 mL of sterile growth media at 37 °C for a maximum of 24 h. Samples were taken at T = 6 h and at T = 24 h, and thermal fluorescence quenching measured at 5 °C increments between 10 and 45 °C over 30 min. 3D excitation-emission matrix (EEM) plots were generated from the fluorescence analyses over time. It was found that the fluorescence of a microbial culture was significantly thermally quenched, but the results were dependent on the fluorophore type and the stage of the bacterial growth curve. Quenching was sometimes non-linear, presumably due to fluorophore production exceeding thermal quenching during the growth phase of the bacteria. Thermal quenching has the potential to allow us to confirm the importance of microbes in fluorescence signals by the non-linear response to increasing temperature, and to utilise the thermal fluorescence quenching properties of molecules to differentiate between fluorophores present during bacterial growth.     

Spectroscopic evidence for triplet excitation energy transfer among carotenoids in the LH2 complex from photosynthetic bacterium Rhodopseudomonas palustris

The LH2 complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (3Car*) has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature (295 K) and at cryogenic temperature (77 K). Broad and asymmetric Tn←T-1 transient absorption was observed at room temperature following the photo-excitation of Car at 532 nm, which suggests the contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (Nc=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main Tn←T1 absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of-1 μs, the same spectral dynamics, however, was not observed at 77 K. The     

Synthesis of homologously pure bacteriochlorophyll-e and f analogues from BChls-c/d via transformation of the 7-methyl to formyl group and self-aggregation of synthetic zinc methyl bacteriopheophorbides-c/d/e/f in non-polar organic solvent

Homologously pure methyl bacteriopheophorbides-e and f (BPhes-e/f_M) were prepared from modification of naturally occurring bacteriochlorophylls-c and d (BChls-c/d), respectively, by transformation of the methyl to formyl group at the 7-position. The absolute configuration of the 1-hydroxyethyl group at the 3-position of (Zn-)BPhes-e/f_M was determined from comparison with structurally known BChl-c/d epimers. Visible spectra of synthetic (Zn-)BPhe-c/d/e/f_M showed that the 7¹-oxidation and the 8²/12¹/20-methylation affected Soret, Q_x and Q_y bands of both the monomeric (in a polar organic solvent) and oligomeric species (in a non-polar solvent).     

Synthesis and antibacterial activity of 4“-O-carbamoyl analogs of clarithromycin

<正>A series of novel 4"-O-carbamoyl analogs of clarithromycin were synthesized and evaluated for their in vitro antibacterial activity. All of the desired compounds showed excellent activity against erythromycin-susceptible S.pneumoniae.Particularly,4-fluorobenzyl carbamate 7a demonstrated potent activity against erythromycin-resistant S.pneumoniae encoded by the mef gene,and remarkably improved activity against erythromycin-resistant S.pneumoniae encoded by the erm gene,and the erm and mef genes.     

Genomic studies on nitrogen metabolism in Halomonas boliviensis: Metabolic pathway,biochemistry and evolution

Halomonas boliviensis LC1^T = DSM 15516^T is a halophilic bacterium that copiously produces osmolytes and polyesters. The growth of H. boliviensis is restricted when glutamate or glutamine is not included in its culture medium. The concentration of glutamate in the medium can regulate the production of either osmolytes or polyesters. However, genomic studies on the nitrogen assimilation have not been performed on H. boliviensis and other members of the family Halomonadaceae. Glutamate metabolism in H. boliviensis was discerned based on genome sequence analysis. The genome sequences of other Halomonadaceae members revealed similar enzymes to those found in H. boliviensis. H. boliviensis and H. elongata DSM 2581^T acquired distinct glutamate dehydrogenase genes through horizontal gene transfer from a different bacterium. Two alleles of glutamine synthetase could be found in H. boliviensis, one of which was obtained from a thermophilic archaeon via horizontal gene transfer. Two subunits of glutamate synthase were also present in H. boliviensis. The small β-subunit had a molecular weight of 52 kDa and was phylogenetically closely affiliated to proteins of other halomonads and Gammaproteobacteria. The large (161 kDa) α-subunit of the halomonads gathered in a separate phylogenetic group, hence glutamate synthase α-subunits of halomonads may be included a novel group of enzymes. Furthermore, putative enzymes obtained from the genome of H. boliviensis should permit complete glutamate metabolism. A similar metabolism should be followed by other halomonads. However, some phenotypic differences between halomonads, such as the ability to assimilate ammonia, resulted as a consequence of horizontal gene transfer. Each enzyme that forms part of the glutamate metabolism in prokaryotes evolved following a different pattern. Yet, most enzymes of halomonads diverged in phylogenetic clusters composed of Proteobacteria, as might be expected.