Nitrous oxide production by cyanobacteria

Evidence is presented here that axenic cultures of Nostoc spp., Aphanocapsa (PCC 6308), and Aphanocapsa (PCC 6714) but not Anacystis nidulans R-2 (PCC 7942) produce N₂O and ammonia when grown on nitrite. The data suggest that the cyanobacteria produce N₂O by nitrite reduction to ammonia.Nonstandard abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethyl urea - NIR nitrite reductase     

Enzymes metabolizing dimethylamine, trimethylamine and trimethylamine N-oxide in the yeast Sporopachydermia cereana grown on amines as sole nitrogen source

Abstract Sporopachydermia cereana , an ascosporogenous yeast, grew on dimethylamine, trimethylamine or trimethylamine N -oxide as sole nitrogen sources and produced mono-oxygenases for dimethylamine and trimethylamine that were significantly more stable than the corresponding enzymes found in Candida utilis . No trimethylamine mono-oxygenase activity was found in S. cereana grown on dimethylamine. In cells grown on trimethylamine N -oxide (but not on the other nitrogen sources), evidence for an enzyme metabolizing the N -oxide, possibly an aldolase, but more probably a reductase was obtained. All these activities showed a similar requirement for the presence of FAD or FMN in the extract buffer during isolation to retain activity. Amine mono-oxygenase activities showed a similar sensitivity to inhibitors, including proadifen hydrochloride and carbon monoxide as the corresponding enzymes in C. utilis . The trimethylamine N -oxide-dependent oxidation of NADH was more sensitive to inhibition by EDTA, N -ethylmaleimide and β-phenylethylamine than the mono-oxygenases, and less sensitive to KCN, and activity was significantly higher with NADPH than was observed with the 2 mono-oxygenases.     

Author idex volume 36 (1986)

Abstract Nitrate reduction to ammonia by marine Vibrio species was studied in batch and continuous culture. In pH-controlled batch cultures (pH 7.4; 50 mM glucose, 20 mM KNO₃), the nitrate consumed accumulated to more than 90% as nitrite. Under these conditions, the nitrite reductase (NO⁻₂→ NH₃) was severely repressed. In pH-controlled continuous cultures of V. alginolyticus with glucose or glycerol as substrates ( D = 0.045 h⁻¹) and limiting N-source (nitrate or nitrite), nitrite reductase was significantly derepressed with cellular activities in the range of 0.7–1.2 μmol min⁻¹ (mg protein)⁻¹. The enzyme was purified close to electrophoretic homogeneity with catalytic activity concentrations of about 1800 nkat/mg protein. It catalyzed the reduction of nitrite to ammonia with dithionite-reduced viologen dyes or flavins as electron donors, had an M _r of about 50 000 (determined by gel filtration) and contained c-type heme groups (probably 4–6 per molecule).     

Structural properties of the proteoliposomes catalyzing electron transport from formate to fumarate

The electron-transport chain catalyzing fumarate reduction by formate has recently been reconstituted from the formate dehydrogenase complex and the fumarate reductase complex from Vibro succinogenes, in a liposomal preparation containing vitamin K-1 (Unden, G. and Kröger, A. (1982) Biochim. Biophys. Acta 682, 258–263). We have now investigated the structural properties of this preparation. The preparation was found to consist of a homogeneous population of unilamellar proteoliposomes with an average diameter of about 100 nm and an internal volume of 2–4 ml / g phospholipid. The buoyant density (1.07 g / ml) was consistent with the protein / phospholipid ratio (0.2 g / g) of the preparation. Leakage of glucose from the internal spaces of the proteoliposomes was negligibly slow. Proteoliposomes prepared with either of the enzyme complexes showed peripheral projections mainly on the outer surface, when examined by electron microscopy after negative staining. The size, orientation and surface density of the projections were consistent with those of the enzymes. Most of the substrate and dye-reactive sites (70–90%) of the enzymes in the proteoliposomes were accessible to external non-permeant substrates. The proteoliposomes catalyzing electron transport were formed by freeze-thawing a mixture of liposomes and protein-phospholipid complexes which did not perform electron transport from formate to fumarate. Nearly the entire amount of the enzymes supplied (0.2 g protein / g phospholipid) was incorporated into the liposomes by this procedure. The transformation of liposomes into proteoliposomes was accompanied by exchange of the internal solutes with the external medium.     

Age-Related Changes in Aldehyde Dehydrogenase Activity of Rat Brain, Liver, and Heart

Abstract: Aldehyde dehydrogenase (ALDH) activity was measured in brains, livers, and hearts of 23–26-month-old and 3-month-old rats. A significant increase of ALDH activity was found in whole brain of old rats with both acetaldehyde (39%) and propionylaldehyde (15%) used as substrates. In different brain areas of old rats, with acetaldehyde used as substrate, a significant increase of ALDH activity was found in striatum (30–50%) and cerebral cortex (37%). However, no significant difference in ALDH activity was found in livers and hearts of young and old rats. Preliminary experiments showed a significant increase of aldehyde reductase activity (52%) with p -nitrobenzaldehyde used as substrate in whole brain of old rats compared with young rats. The present work indicates that an increase of ALDH activity in brain of old rats may be an adaptive phenomenon.     

Increase in nitrate reductase activity in the presence of sucrose in bean leaf segments

The supply of sucrose to leaf segments from light-grown bean seedlings caused a substantial increase in substrate inducibility of in vivo and in vitro nitrate reductase activity but only a small increase in total protein. Cycloheximide and chloramphenicol inhibited the increase in enzyme activity by nitrate and sucrose. The in vivo decline in enzyme activity in nitrate-induced leaf segments in light and dark was protected by sucrose and nitrate. The supply of NADH also protected the decline in enzyme activity, but only in the light. In vitro stability of the extracted enzyme was, however, unaffected by sucrose. The size of the metabolic nitrate pool was also enhanced by sucrose. The experiments demonstrate that sucrose has a stimulatory effect on activity or in vivo stability ' of nitrate reductase in bean leaf segments, which is perhaps mediated through increased NADH level and/or mobilization of nitrate to the metabolic pool.     

Mode of interference of chlorosis-inducing herbicides with peroxisomal enzyme activities

In rye leaves ( Secale cereale L. cv. Petkus "Kustro") bleached in the presence of the chlorosis-inducing herbicides aminotriazole, haloxidine, San 6706 or difunone in white light of 54.2 W m^-2 (5000 lx), catalase activity was very low. In addition, the activities of glycolate oxidase and hydroxypyruvate reductase were strongly diminished in treatments with San 6706 and difunone. The lowering of the peroxisomal enzyme activities was observed in red, but not in blue light and did not occur after treatment with the non-bleaching pyridazinone derivative San 9785. The deficiencies of the peroxisomal enzymes did not appear to be involved in the initiation of the chlorosis. Instead they are probably produced as secondary consequences of the bleaching. Low peroxisomal enzyme activities were also obtained without herbicide treatment by growing the leaves in an atmosphere of 2% O₂ and 3% CO₂, but in this case were not accompanied by an increased sensitivity of the Chl to photooxidative bleaching. The peroxisomal enzymes reached as high activities as in untreated controls when the herbicide-treated leaves were grown at a low light intensity of 0.106 W m^-2 (10 lx). After transfer of herbicide-treated leaves grown under 0.106 W m^-2 to 306 W m^-2 (30 000 lx), catalase was strongly inactivated, even at 0°C. In treatments with San 6706 and difunone the increase of the activities of glycolate oxidase and hydroxypyruvate reductase was either stopped, remaining unchanged, or the enzymes were slightly inactivated after exposure to 306 W m^-2 (30 000 lx). The observations suggest that the inactivation of peroxisomal enzymes results from photooxidative events in the chloroplasts.     

Effect of auxin on the metabolism of mevalonic acid in suspension-cultured carrot cells

The rate of incorporation of [¹⁴C]mevalonate into carotenoid and steroid fractions in suspension-cultured carrot cells decreased markedly after 2,4-dichlorophenoxyacetic acid was removed from the medium. In parallel to this change, the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in a microsomal fraction was reduced to ca 33% of the control value, while that of a particulate fraction showed no significant change. The activities of mevalonate activating enzymes remained unchanged after auxin deprivation.     

HBsAg重组DNA转化中国地鼠卵巢细胞二氢叶酸还原酶阴性突变株的细胞染色体变化及致瘤性

整合了含乙型肝炎病毒表面抗原(HBsAg)基因和dhfr基因的CHO-dhfr~-细胞,其染色体的畸变率和畸变类型都比亲代CHO-dhfr~-细胞高。但转化前后两系细胞的重要特性都未发生变异,即两者的染色体总数无差别,都是20条。两系细胞株接种裸鼠,均未发现有致瘤性。