Proton n.m.r. of ferredoxin from Clostridium pasteurianum

Proton magnetic resonance spectra at 500 MHz are reported for the oxidized and reduced forms of the 2[4Fe-4S]-ferredoxin from Clostridium pasteurianum. The reduced protein showed additional peaks in the 10–60 ppm region, which were previously unobserved, and there were significant differences between oxidized and reduced states in the whole region. The electron exchange rate in partially reduced ferredoxin is slow on the n.m.r. time scale when reduced with sodium dithionite, but fast when zinc reduced methyl viologen is used as reducing agent. We explain the difference between fast and slow exchange as being due to the different chemical properties of the two reducing agents.     

Proton n.m.r. of ferrodoxin from Clostridium pasteurianum

Proton magnetic resonance spectra at 500 MHz are reported for the oxidized and reduced forms of the 2[4Fe-4S]-ferredoxin from Clostridium pasteurianum. The reduced protein showed additional peaks in the 10–60 ppm region, which were previously unobserved, and there were significant differences between oxidized and reduced states in the whole region. The electron exchange rate in partially reduced ferredoxin is slow on the n.m.r. time scale when reduced with sodium dithionite, but fast when zinc reduced methyl viologen is used as reducing agent. We explain the difference between fast and slow exchange as being due to the different chemical properties of the two reducing agents.     

Mathematical modelling of dynamics and control in metabolic networks. I. On Michaelis-Menten kinetics

As a starting point for modeling of metabolic networks this paper considers the simple Michaelis-Menten reaction mechanism. After the elimination of diffusional effects a mathematically intractable mass action kinetic model is obtained. The properties of this model are explored via scaling and linearization. The scaling is carried out such that kinetic properties, concentration parameters and external influences are clearly separated. We then try to obtain reasonable estimates for values of the dimensionless groups and examine the dynamic properties of the model over this part of the parameter space. Linear analysis is found to give excellent insight into reaction dynamics and it also gives a forum for understanding and justifying the two commonly used quasi-stationary and quasi-equilibrium analyses. The first finding is that there are two separate time scales inherent in the model existing over most of the parameter space, and in particular over the regions of importance here. Full modal analysis gives a new interpretation of quasi-stationary analysis, and its extension via singular perturbation theory, and a rationalization of the quasi-equilibrium approximation. The new interpretation of the quasi-steady state assumption is that the applicability is intimately related to dynamic interactions between the concentration variables rather than the traditional notion that a quasi-stationary state is reached, after a short transient period, where the rates of formation and decomposition of the enzyme intermediate are approximately equal. The modal analysis reveals that the generally used criterion for the applicability of quasi-stationary analysis that total enzyme concentration must be much less than total substrate concentration, et much less than St, is incomplete and that the criterion et much less than Km much less than St (Km is the well known Michaelis constant) is the appropriate one. The first inequality (et much less than Km) guarantees agreement over the longer time scale leading to quasi-stationary behavior or the applicability of the zeroth order outer singular perturbation solution but the second half of the criterion (Km much less than St) justifies zeroth order inner singular perturbation solution where the substrate concentration is assumed to be invariant. Furthermore linear analysis shows that when a fast mode representing the binding of substrate to the enzyme is fast it can be relaxed leading to the quasi-equilibrium assumption. The influence of the dimensionless groups is ascertained by integrating the equations numerically, and the predictions made by the linear analysis are found to be accurate.(ABSTRACT TRUNCATED AT 400 WORDS)     

Actinomadura mexicana sp. nov. and Actinomadura meyerii sp. nov., two novel soil sporoactinomycetes

The taxonomic position of two soil isolates, strains A288(T) and A290(T) [provisionally assigned to the genus Actinomadura] was clarified in a polyphasic study. The organisms showed a combination of chemotaxonomic and morphological properties typical of actinomadurae. They also formed distinct phyletic lines in the 16S rRNA Actinomadura gene tree; strain A288(T) was associated with A. nitritigenes whereas strain A290(T) was closely related to a group that consisted of A. citrea, A. coerulea, A. glauciflava, A. luteofluorescens and A. verrucosospora. Strains A288(T) and A290(T) showed key phenotypic features which readily distinguish them from one another and from representatives of related validly described species of Actinomadura. It is proposed that the two organisms be classified as new species of the genus Actinomadura. The names proposed for the new taxa are Actinomadura mexicana (A290(T) = DSM 44485(T) = NRRL B-24203(T)), and Actinomadura meyerii (A288(T) = DSM 44485(T) = NRRL B-24203(T)).     

Chloroplast and cytoplasmic enzymes 1, 2, 3. Subunit structure of pea leaf aldolases.

The pea leaf chloroplastic and cytoplasmic forms of aldolase are very similar in structure. The subunit molecular weights determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate are approximately 37.000. Both aldolases appear to terminate in the same sequence, SerAlaTyrCOOH, and the amino-terminal sequence H₂NGlySerTyrAla was obtained for each. The previously reported differences in kinetic properties and in isoelectric points of the two pea leaf enzymes probably are the consequence of minor differences in amino acid composition or conformation.     

Genetics of aliphatic glucosinolates. IV. Side-chain modification in Brassica oleracea

The biochemical and genetical relationship between aliphatic glucosinolates which have methylthioalkyl, methylsulphinylalkyl and alkenyl side chains has not been resolved by biochemical studies. In this study, two hypothetical models are tested by the genetic analysis of a backcross population between Brassica drepanensis and B. atlantica. The results support one of the models in which 3-methylthiopropyl glucosinolate is sequentially converted to 3-methylsulphinylpropyl, and then to 2-propenyl glucosinolate, by the action of dominant alleles at two loci. RFLP mapping positioned both loci on the same linkage group homologous to the B. napus N19 linkage group. The implication of the results for the genetic manipulation of glucosinolates in Brassica to improve flavour and nutritional properties, and in order to investigate plant-insect interactions, is discussed.     

Chicken fumarase. II. Kinetic studies.

The catalysis of the hydration of fumarate and deshydration of L - malate by chicken fumarase was measured spectrophotometrically over a range of substrate concentrations from 4 times 10(-3) M to 8 times 10(-5) M for fumarate and from 8 times 10(-2) M to 10(-3) M for L - malate. For the forward and reverse reactions, linear Lineweaver and Burk plots were obtained. The Michaelis constants and the maximum initial velocities for both substrates were determined and the Haldane relation was found to be obeyed. The effect of pH on activity was investigated over a pH range from 5.5 to 9.0 and the data indicate the presence, in the active site, of two ionizable groups, one in the acidic form and one in the basic form. The values of the ionization constants, determined for the enzyme - substrate complexes, agree closely with the ones obtained for the porcine enzyme. The mode of action of twenty-four structural analogs on the initial velocity of the dehydration of L-malate, by chicken fumarase was examined. From these studies, two regions positively charged appear necessary for the effective binding of the carboxylates of the substrates and competitive inhibitors to the active center. Moreover, the data suggest the presence of an additional group, in the catalytic site of chicken fumarase, that stabilizes the carbon-carbon double bond common to fumarate and its structural analogs. Finally, from the comparison of the kinetic properties of the chicken and pig fumarases, it may be concluded that the catalytic mechanism of the homologous enzymes are very similar, if not identical.     

Studies on Diterpenoids ot Rabdosia macrocalyx var. jiuhua Z. W. Xue et X. W. Wang

Four diterpenoids have been isolated from the dried leaves of Rabdosia macrocalyx var. juihua Z. W. Xue et X..W. Wang. Three of them were shown to be known diter- penoids, excisanin A, excisanin B and macrocalyxin A, while the one, a new kauranetype diterpene, was named jiuhuanin A. On the basis of physico-chemical constants, spectroscopic analysis of the new compound and properties of its derivatives, the structure of the compound was identified as (1). Jiuhuanin A was shown to have cytotoxicity in vitro against cultures of Hela cell and A549 cells.     

Purification and some properties of free and cell-associated dextransucrase from Streptococcus sanguis.

Dextransucrase of Streptococcus sanguis occurred in cell-free and cell-associated forms. Cell-free dextransucrase was purified by four successive chromatographies on Bio-Gel P 60, DEAE-cellulose, and Bio-Gel P 200 from the culture supernatant. The purification of cell-associated dextransucrase was made from the pellet of Streptococcus sanguis culture. Bacterial pellet was extracted with 1 M phosphate buffer (pH 6.0) and chromatographied by using an immunosorbent column. The two enzymes gave single bands in polyacrylamide gel electrophoresis. The molecular weight determined by sodium dodecyl sulfate polyacrylamide gel was about 100 000 daltons for the two forms of dextransucrases. The optimum pH of the cell-free and cell-associated enzymes was around 6 and the temperature optimum was broad for the two enzymes. The KM values for sucrose were respectively 2 mM and 3 mM for cell-free and cell-associated enzymes. When primer dextran was added, the reaction velocity increased but the KM for sucrose remained the same, and the KA for dextran was 200 muM for the two dextransucrases. Trehalose and maltose acted also as glucosyl residue acceptors. Purified enzymes had dextran synthesising activity and invertase-like activity. The same properties of the two forms of enzymes and the positive cross reaction against anti free and anti cell-associated globulins stongly suggest the identity of the two enzymes.     

Sequences of the 1.672 g/cm3 satellite DNA of Drosophila melanogaster.

The 1.672 g/cm³ satellite DNA of Drosophila melanogaster was purified by successive equilibrium centrifugations in a CsCl gradient, an actinomycin $\text{D}\text{CsCl}$ gradient, and a netropsin sulfate/CsCl gradient. The resulting DNA was homogeneous by the physical criteria of thermal denaturation, renaturation kinetics and equilibrium banding in each of the gradients listed above. In addition, the complementary strands could be separated in an alkaline CsCl gradient. Despite this rigorous purification procedure, nucleotide sequence analysis indicates the presence of two different DNA species in this satellite, poly $\text{A-A-T-A-T}\text{T-T-A-T-A}$ and poly$\text{A-A-T-A-T-A-T}\text{T-T-A-T-A-T-A}$. Further physical, chemical and template properties of the isolated complementary strands demonstrate that these two repeating sequences are not interspersed with each other. This result has biological significance since sequences of this particular satellite are known to be located primarily on two different chromosomes, Y and 2. These results further suggest that the sequence heterogeneity observed in satellite DNA of higher eukaryotes may result from mixtures of very closely related but molecularly homogeneous repeated sequences each restricted to a particular chromosome or chromosomal region.     

Pig heart mitochondrial ATPase : properties of purified and membrane-bound enzyme. Effects of flavonoids.

Soluble ATPase (F1) has been purified from pig heart mitochondria. The purified enzyme had a high specific activity and was homogeneous as checked by ultracentrifugation and electrofocusing. It could be dissociated into subunits by cold-treatment or sodium dodecyl sulfate denaturation. The molecular weights of the two major and three minor subunits could be estimated by sodium dodecyl sulfate gel electrophoresis. The native enzyme had an isoelectric point of 5.2 while the cold-denatured enzyme showed three main bands focusing at pH 5.0, 5.2, and 5.4. Kinetic properties (Vm and Km (atp) have been compared for the soluble and membrane bound ATPase in presence of various anions. Inhibitory effects of Quercetin and other flavonoids have been tested in order to get an insight on the interaction between ATPase and its natural inhibitor.     

落叶松人工林凋落物与土壤肥力变化的研究

以东北东部山区帽儿山实验林场落叶松人工林作为研究对象,从林地凋落量、林地凋落物归还量、凋落物层现存量以及土壤理化性质的变化等方面,研究了经抚育间伐后不同年龄阶段同一落叶松林分土壤肥力的变化以及间伐与未间伐林分土壤理化性质的差异．结果表明,落叶松人工林凋落量和以凋落物形式归还于林地的营养元素呈现出随年龄增加而增长的总趋势．经抚育间伐后,由于阔叶树种的引入使凋落物的组成结构发生变化,凋落物层的分解率逐步提高,加速了凋落物中营养物质的释放和归还,减缓了凋落物积累与分解的矛盾,提高了落叶松人工林的土壤肥力．１５年间土壤有机质、全Ｎ和全Ｐ２Ｏ５平均值分别增长了３５２．００％、２２５．５３％和３４．９６％．间伐后的落叶松人工林土壤的理化性质得到不同程度的改善．     

Rhodococcus aetherivorans sp. nov., a new species that contains methyl t-butyl ether-degrading actinomycetes

The taxonomic positions of two actinomycetes, strains Bc663 and 10bc312T, provisionally assigned to the genus Rhodococcus were determined using a combination of genotypic and phenotypic properties. The organisms have phenotypic properties typical of members of the genus Rhodococcus and were assigned to the 16S rRNA subgroup which contains Rhodococcus rhodochrous and closely related species. The two strains, which have many phenotypic features in common, belong to the same genomic species albeit one readily separated from Rhodococcus ruber with which they form a distinct phyletic line. The organisms were also distinguished from all of the species classified in the R. rhodochrous subgroup, including R. ruber, using a combination of phenotypic properties. The genotypic and phenotypic data show that strains Bc663 and 10bc312T merit recognition as a new species of Rhodococcus. The name proposed for the new species is Rhodococcus aetherivorans (10bc312T = DSM 44752T = NCIMB 13964T).     

长筒石蒜鳞茎中的生物碱类成分(英文)

从长筒石蒜鳞茎的乙醇提取物中分离得到7个生物碱类化合物,经理化方法和波谱分析,分别鉴定为galanthamine(1),lycoramlne(2),6β-hydroxycrinamine(3a),6α-hydroxycrinamine(3b),(-)-amarbellisine(4),tazettine(5),macowine(6).其中化合物3a～6为首次从该植物中分离得到.     

半干旱地区河滩宜林地立地条件研究

采用对应分析、回归分析方法对半干旱地区河滩宜林地土壤基本性质进行了研究．结果表明,河滩地土壤理化性质的差异主要表现为土壤质地的差异,有机质含量、ＣａＣＯ３含量、全盐量、田间持水量等与土壤机械组成中细粒级含量（尤其是＜０．００１ｍｍ、０．００１～０．００５ｍｍ两个粒级）呈正相关．半干旱地区河滩宜林地立地条件主导因子为地下水位、土壤质地和有效土层厚度．采用最优分割法对地下水位、有效土层厚度进行了分级．以主导因子分级组合法综合考虑当地具体情况,将河滩宜林地划分为２０个立地类型,并对其进行了多树种综合评价．     

Two distinct adhesion mechanisms in embryonic neural retina cells. II. An immunological analysis

Antibodies were raised against neural retina cells prepared by dissociation in EGTA alone (E cells, Ca²⁺-independent aggregation), in trypsin + Ca²⁺ (TC cells, Ca²⁺-dependent aggregation), or in trypsin + EGTA (TE cells, nonadhesive). Anti-E-cell Fab selectively inhibited Ca²⁺-independent aggregation, anti-TC-cell Fab selectively inhibited Ca²⁺-dependent aggregation, and anti-TE-cell Fab inhibited neither. Fab from a fourth preparation, also raised against E cells, inhibited both Ca²⁺-independent and Ca²⁺-dependent aggregation but was separated by immunoadsorption into two fractions, one specific for each mode of aggregation. In cells which utilize both modes simultaneously (LTC cells), each was inhibited exclusively by the appropriate Fab. The immunological data presented here demonstrate the existence in the same cells of two distinct and functionally independent adhesion mechanisms, each responsible for one of the two modes of aggregation. The differing adhesive properties of retinal cells prepared by different procedures are explained by the presence, absence, or degree of activity of these two mechanisms, qualities regulated by the concentrations of trypsin and Ca²⁺ used in the tissue dissociation.     

alpha-Galactosidase (melibiase) from Saccharomyces carlsbergensis: structrual and kinetic properties.

This report describes structural and kinetic properties of the purified α-galactosidase from Saccharomyces carlsbergensis. This galactosidase has many similar properties to other exocellular enzymes in yeast which have been reported. Its molecular weight of 300,000 is comparable; it has similar carbohydrate content (57%) and amino acid and carbohydrate composition. That is, 35% of its amino acid residues can be accounted for by threonine, serine, and aspartic acid. Its carbohydrate composition is primarily mannose (90–95%) with approximately 7% glucose and 1% glucosamine. The enzyme is very stable to both acidic and alkaline conditions as well as to heating to 50 °C. α-Galactosidase remains active after incubation with as much as 1% sodium dodecyl sulfate at 30 °C. However, the enzyme is denatured with urea and guanidine hydrochloride. The loss of activity is proportional to the urea concentration, the nondenatured enzyme being responsible for the remaining activity. Inactivation by urea is partially reversible. With urea or 60 °C heat denaturation, the enzyme dissociates into two types of subunits as revealed by polyacrylamide gel electrophoresis with sodium dodecyl sulfate. Thus, α-galactosidase is the first external enzyme from yeast in which an oligomeric structure is reported. The enzyme catalyzes the hydrolysis of p-nitrophenyl-α-d-galactoside, melibiose, and raffinose with similar pH optima and V_max. However, the affinity is 20-fold lower for raffinose than for the other two substrates. Sugars having the same configuration in carbons 2, 3, and 4 as galactose competitively inhibit the enzyme.     

菜心溶菌酶的提纯及酶学性质

菜心（ＢｒａｓｓｉｃａｃａｍｐｅｓｔｒｉｓＬ．ｓｓｐ．ｃｈｉｎｅｎｓｉｓｖａｒ．ｕｔｉｌｉｓ）叶子高速捣碎后,滤液经酸碱处理,硫酸铵分步沉淀,凝胶柱层析等步骤分离纯化溶菌酶,酶比活力达３４１４．６Ｕ／ｍｇ,纯化倍数为１９７．４。菜心溶菌酶在较宽的温度或ｐＨ值范围均有活性,最适温度为６０℃,最适ｐＨ值为５．８,底物Ｋｍ值为８７μｇ／ｍＬ。该酶对热和酸碱的稳定性较高,巯基和酪氨酸残基不是该酶活性中心的必需基团。     

大穗黑麦草抗性的有关生理生化指标的研究

通过对大穗黑麦草生物学性状观察及测定叶绿素含量 ,丙二醛含量 ,抗坏血酸氧化酶活性等生理生化指标 ,并与湖北省当前推广的小麦品种鄂恩 1号、鄂恩 4号作比较 ,结果表明它具有较高的抗性 ,为小麦的抗性育种提供了新的野生种资源     

E. coli RNAase P has a required RNA component

RNAase P has been partially purified from three thermosensitive strains of E. coli and the thermal inactivation characteristics of each preparation have been determined. The RNAase P preparations from two of these mutant strains, ts241 and ts709, and the wild-type strain have been separated into RNA and protein components. Various mixtures of the reconstituted components have been checked in vitro for complementation of their thermal sensitivity properties. The protein component of RNAase P from ts241 and the RNA component of RNAase P from ts709, respectively, account for the thermal sensitivity of the rnaase P from the two strains. The amount of the RNA component of RNAase P is lower in ts709 than in ts241 or the wild-type parent, 4273. RNAase P partially purified from a revertant of the third mutant strain, A49, which maps at or near the ts241 mutation, has an altered charge when compared to the RNAase P from the parent strain, BF265. We conclude that mutations which affect either the protein or RNA component of RNAase P can confer thermal sensitivity on the enzyme both in vivo and in vitro.