Conversion of potato phosphorylase isozymes

The conversion of a slow moving potato phosphorylase isozyme to a fast one, in sprouting tubers, either on freezing the whole tubers or on storage of their crude extracts, is due to limited proteolysis. High protease inhibitor concentration seems to be the primary factor preventing this conversion in freshly harvested tubers under similar conditions. Though MW determinations on both isozymes show the removal of a peptide during conversion, it is also likely that the enzyme may take up a different conformation due to the removal of this peptide.     

α-1,4-Glucan phosphorylase forms in the green alga Eremosphaera viridis

In extracts of the unicellular green alga Eremosphaera viridis DeBary (Chlorococcales, Chlorophyceae) the average specific activity of α-1,4-glucan phosphorylase (E.C. 2.4.1.1) was 200 nmol glucose 1-phosphate formed per min and mg protein. Using continuous and discontinuous electrophoresis on polyacrylamide gels, three phosphorylase forms were found. When the log of the relative mobility of the three enzyme forms was plotted versus the acrylamide gel concentration (Ferguson plot) parallel lines were obtained, indicating that the three enzymes were indiscernible with respect to molecular weight. Electrophoresis on density gradient gels resulted in three activity zones lying close to each other. The relative molecular mass ( M _r) of the three enzymes was estimated to be around 180,000 with a difference of less than 7,000 between the small and the large forms.     

Purification and properties of α-1,4-glucan phosphorylase from the red seaweed Gracilaria sordida (Gracilariales)

α-1,4-Glucan phosphorylase (EC 2.4.1.1) from the red seaweed Gracilaria sordida (Harv.) W. Nelson was adsorbed onto starch-Sepharose 6B and Sephacryl S-300 under specified conditions. The algal enzyme was purified to homogeneity by these two steps. A molecular weight of 97.4 kDa was observed on SDS-polyacrylamide gel electrophoresis under reducing conditions, while the native molecular weight was 240 kDa asrevealed by 8-25% native gradient gel electrophoresis or 245 kDa by gel filtration. The pI of the enzyme was 5.4. It had a Km of 227, 264, 285, and 453 μg ml-1, respectively, towards glycogen, amylopectin, amylose, and maltodextrin. The enzyme activity was inhibited by cyclohexaamylose, ADP-glucose, and UDP-glucose. In contrast to other plant sources, cell-free extracts of G. sordida contained only one form of phosphorylase.     

Subcellular immuno-localization, amino acid composition and partial amino acid sequences of α-l,4-glucan phosphorylase of Gracilaria spp (Rhodophyta)

Antibodies have been raised against an α-l,4-glucan phosphorylase (EC 2. 4. 1. 1) purified from the red alga Gracilaria chilensis. Localization of α-l,4-glucan phosphorylase in thin sections of G. chilensis and G. tenuistipitata was performed using immuno-gold labelling and transmission electron microscopy. The enzyme was localized in the cytosol and around the cytosolic starch granules of the algal cells. The labelling was not associated with the chloroplast or the cell wall. Amino acid composition of the red algal phosphorylase was quite similar to that of potato tuber and rabbit muscle phosphorylases. Partial amino acid sequences showed 48, 54 and 65% homology with the rabbit, potato and Escherichia coli enzymes, respectively.     

The biosynthesis of phycocyanobilin in Anacystis nidulans

Aminolevulinic acid, the common precursor of linear and cyclic tetrapyrroles, can arise either by condensation of succinate and glycine or from the ent     

The role of modelling in the control of toxic blue-green algae

Blooms and scums of blue-green algae (cyanobacteria)have occurred throughout the world for many years andare only one of many problems associated withover-enrichment by nutrients of fresh and marinewaters. Although much studied and written about,eutrophication poses complex and difficult managementproblems. The role of modelling as an aid to thecontrol of blue green algae is discussed.     

Comparison of the long-wave chlorophyll fluorescence in various green and blue-green algae and diatoms

Two types of long-wave fluorescence bands with similar band shape occur at room temperature in various algae: F_II700 and F_I715. F_II700 occurs in a limited number of algae, follows PS II transients, increases with culture age and is moderately increased by cooling to 83 K. F_I715 occurs in most algae, especially Anabaena, but much less in most diatoms and Tribonema. It does not follow PS II transients, does not increase with culture age and is much increased by cooling to 83 K.An interpretation for the characteristics of F_II700 and F_I715 is given.     

The b.e. and Q types of 1,4-α-d-glucan: 1,4-α-d-glucan-6-glucosyltransferase isozymes in algae

The branching isozymes of the red alga, Rhodymenia pertusa are of two types: Q, which can branch, via the synthesis of α-1,6-glucosyl linkages, linear amyloses to amylopectin; and b.e., which can further branch the amylopectin formed to the more highly-branched floridean starch. Using the technique of tandem crossed-immunoelectrophoresis, it is shown that the Q branching isozyme of the red alga is more closely related to the b.e. type of branching isozymes of Anacystis nidulans and Cyanidium caldarium than it is to the exclusively Q types of branching isozymes found in Chlorella pyrenoidosa and other chlorophytes. The possibility of a biphyletic evolution of the red and the green algae from blue-green ancestral forms is discussed.     

Tetrapyrrole biosynthesis in Anacystis nidulans; incorporation of [1-13C]-, [2-13C]-, [1,2-13C]- and [2-13C, 2-2H3]acetate

Labelling experiments with [2-¹³C]- and [1,2-¹³C]acetate showed that both photopigments of Anacystis nidulans, chlorophyll a and phycocyanobilin, share a common biosynthetic pathway from glutamate. The fate of deuterium during these biosynthetic events was studied using [2-¹³C, 2-²H₃]acetate as a precursor and determining the labelling pattern by ¹³C NMR spectroscopy with simultaneous [¹H, ²H]-broadband decoupling. The loss of ²H (ca 20%) from the precursor occurred at an early stage during the tricarboxylic acid cycle. After formation of glutamate there was no further loss of ²H in the assembly of the cyclic tetrapyrrole intermediates or during decarboxylation and modification of the side-chains. Thus the labelling data support a divergence in the pathway to cyclic and linear tetrapyrroles after protoporphyrin IX.     

Cellulose and callose of the pollen tube wall of Camellia japonica

By chemical analyses in addition to IR spectroscopy and staining reactions, cellulose and a β-1,3-glucan (callose) were demonstrated to occur in the     

A Historical Perspective for the Catalytic Reaction Mechanism of Glycosidase; So As to Bring about Breakthrough in Confusing Situation

Various catalytic reaction models have been proposed as the reaction mechanisms of glycosidases, but a reasonable and unitary model capable of interpreting both “inverting” and “retaining” glycosidase reactions remains to be established. As for the models proposed to date, the nucleophilic displacement mechanism and the oxocarbenium ion intermediate mechanism are widely known, but recently the former is widely accepted, and so the general tendency of world opinion appears to favor it. This reaction model, however, is considered to comprise some inconsistencies that cannot be neglected from the viewpoint of reactivity in organic chemistry. While the nucleophilic displacement mechanism is often applied to reactions of glycosidases, it appears unlikely that such reactions actually occur. This review argues that the oxocarbenium ion intermediate reaction mechanism is more rational than the nucleophilic displacement reaction mechanism, as the action mode of glycosidases and related enzymes.     

Effect of growth and subsequent decomposition of blue-green algae on the transformation of iron and manganese in submerged soils

N₂-fixing blue-green algae (Cyanobacteria), besides enriching soils with N and organic carbon, may modify a number of chemical and electro-chemical properties of the soils resulting in a change in availability of some micronutrient elements. Keeping this in view, an experiment was conducted to study the effects of growth and subsequent decomposition of blue-green algae on changes in the different forms of Fe and Mn in four soils under submerged condition. A mixed algal culture containing Anabaena, Nostoc, Cylindrospermum, and Tolypothrix was used as inoculum. It was allowed to grow for 2 months, after which the soils were sequentially extracted with (i) M NH₄OAc (pH 7.0), (ii) M K₄P₂O₇, (iii) 0.1 M NH₂OH.HCl (pH 2.0), (iv) 0.2 M (NH₄)₂C₂O₄ (pH 3.0) and (v) 0.1 M ascorbic acid to obtain water-soluble plus exchangeable, organically bound, easily reducible, amorphous oxides-and crystalline oxides-bound forms of Fe and Mn, respectively, both during the growth as well as the subsequent in-situ decomposition of the algal biomass in soils. Iron and Mn in the extracts were estimated by atomic absorption spectrophotometry.The results showed that growth of blue-green algae in submerged rice soils caused a decrease in the NH₄OAc-extractable forms of Fe and Mn with concomitant increases in all the other four determined forms of the elements. Such decreases and/or increases in different forms of Fe and Mn in soils were explained as being due to release of O₂, addition of organic matter and liberation of extracellular organic compounds by the blue-green algae during their growth. The decomposition of algal biomass resulted in an increase in the NH₄OAc-, K₄P₂O₇- and (NH₄)₂C₂O₄-extractable forms of Fe and Mn with a simultaneous decrease in the NH₂OH · HCl- and ascorbic acid-extractable forms. Development of strong reducing conditions and formation of organic acids with chelating properties were suggested as being the cause of the above changes. The implication of these changes in the forms of Fe and Mn for the Fe and Mn nutrition of rice plants were discussed.     

A greenhouse study on the effect of inoculation of N-fixing blue-green algae in an alluvial soil treated with P and Mo on the yield of rice and changes in the N-content of soil

Summary The efficiency of the inoculation of three cultures of N-fixing blue-green algaeviz. (i)Aulosira fertilissima (A₁), (ii)Nostoc muscorum (A₂) and (iii) their mixture (A₃) in increasing the grain and straw yield of rice, nitrogen uptake in grain and nitrogen content in soil was studied in a green house experiment with an alluvial soil in presence or absence of urea nitrogen application. Inoculation significantly increased the grain and straw yield of rice and nitrogen uptake in grain, but the efficiency of inoculation gradually decreased with the increase in the levels of urea nitrogen application, the extent of decrease varying with the algal cultures inoculated. The nitrogen content in the soils after the crop harvest recorded a significant increase due to inoculation but after air drying the soil a marker decrease of the same was observed, which indicated that most of the nitrogen added to the soil by blue-green algae through fixation did not persist after air drying the soil.     

Chemical composition of the cell walls of Lolium multiflorum endosperm

Cell walls isolated from Lolium multiflorum endosperm grown in liquid suspension culture contain 90% carbohydrate (as anhydro-glucose), 0·3 nitrogen, 1·9% lipid and 4·3% ash. The relative proportions of neutral sugars present in hydrolysates of the wall polysaccharides are glucose, 50%; arabinose, 19%; xylose, 26% and galactose, 5%. Extraction of the wall with 7 M urea solubilizes a polysaccharide representing 19% of the wall and composed of glucose and minor amounts of pentoses. This fraction has been examined by acid and enzymic hydrolysis and by periodate oxidation, and was shown to be a β-1,3; 1,4-glucan with approx. 79% 1,4-linkages. A specific β-glucan hydrolase has been used to determine the content of this mixed-linked glucan in isolated endosperm cell walls.     

Intraspecies evolution of enzymic mechanisms associated with the synthesis of α-1,4 storage glucans in two thermophilic-acidophilic algae of Cyanidium type

Cyanidium caldarium is an enigmatic eukaryotic alga which is both acidophilic and thermophilic. Its taxonomic position has been in doubt and, hence     

铅对蟾蜍肝、肾过氧化物酶和酯酶同工酶的影响

以腹腔注射法对蟾蜍 (Bufobufogargarizans)给铅 ,处理 7d后 ,使用聚丙烯凝胶垂直平板电泳法 ,研究了不同浓度 (按铅计 1、2、4、8mg·kg-1 体重 )的铅对蟾蜍肝脏、肾脏过氧化物酶和酯酶同工酶的影响。结果表明 ,不同浓度的铅均可使肝、肾组织过氧化物酶同工酶带强弱发生明显变化 ;对肝、肾酯酶同工酶的影响表现出一定的组织差异性 ,且在一定范围内主要表现为应激性 ,即低剂量的铅可诱导酶活性的提高。     

Substrate specificity of E. coli uridine phosphorylase. Further evidences of high-syn conformation of the substrate in uridine phosphorolysis

Twenty five uridine analogues have been tested and compared with uridine with respect to their potency to bind to E. coli uridine phosphorylase. The kinetic constants of the phosphorolysis reaction of uridine derivatives modified at 2′-, 3′- and 5′-positions of the sugar moiety and 2-, 4-, 5- and 6-positions of the heterocyclic base were determined. The absence of the 2′- or 5′-hydroxyl group is not crucial for the successful binding and phosphorolysis. On the other hand, the absence of both the 2′- and 5′-hydroxyl groups leads to the loss of substrate binding to the enzyme. The same effect was observed when the 3′-hydroxyl group is absent, thus underlining the key role of this group. Our data shed some light on the mechanism of ribo- and 2′-deoxyribonucleoside discrimination by E. coli uridine phosphorylase and E. coli thymidine phosphorylase. A comparison of the kinetic results obtained in the present study with the available X-ray structures and analysis of hydrogen bonding in the enzyme-substrate complex demonstrates that uridine adopts an unusual high-syn conformation in the active site of uridine phosphorylase.     

球状绿藻的隐性生物多样性及其分类学进展

球状绿藻主要指绿藻门中多为单细胞, 形状为球形、近球形, 或由球形衍生出来的其他形状的藻类。球状绿藻分布广泛, 遍布全球, 生活于淡水、海水和亚气生等生境中, 其相似的简单形态下隐藏着复杂的物种多样性。球状绿藻分类学上主要位于绿藻门的两纲四目及其一些独立支系的类群。球状绿藻分类学正由传统的基于形态特征向基于分子信息的复合分类方法转变。球状绿藻隐性的物种多样性涉及约40属, 其中15属是依据新标本材料而建立的新属, 12个属是依据新证据建立的新组合。本文重点介绍了1998年以后在共球藻纲和绿藻纲中新发现和命名的单细胞球状绿藻, 介绍了它们的形态特征、分类学迁移及理由, 特别对常见的小球藻属和栅藻属的分类学概念变迁作了详细介绍, 对一些尚没有中文名的拉丁学名给出了中文命名。另外, 本文讨论了基于DNA的分类学方法在球状绿藻分类学中的应用, 目前系统发育位置的不同已经成为球状绿藻分类的主要依据。目前球状绿藻分类面临的问题是大多分类位置未用分子系统发育方法的验证。 未来, 球状绿藻分类学家应用系统发育研究结合形态学研究探索单细胞球状绿藻的生物多样性。