Effects of winter flooding on phosphorus dynamics in rice fields

Limnology - Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter...     

Isobutanol production from cellobiose in Escherichia coli

Converting lignocellulosics into biofuels remains a promising route for biofuel production. To facilitate strain development for specificity and productivity of cellulosic biofuel production, a user friendly Escherichia coli host was engineered to produce isobutanol, a drop-in biofuel candidate, from cellobiose. A beta-glucosidase was expressed extracellularly by either excretion into the media, or anchoring to the cell membrane. The excretion system allowed for E. coli to grow with cellobiose as a sole carbon source at rates comparable to those with glucose. The system was then combined with isobutanol production genes in three different configurations to determine whether gene arrangement affected isobutanol production. The most productive strain converted cellobiose to isobutanol in titers of 7.64?±?0.19 g/L with a productivity of 0.16 g/L/h. These results demonstrate that efficient cellobiose degradation and isobutanol production can be achieved by a single organism, and provide insight for optimization of strains for future use in a consolidated bioprocessing system for renewable production of isobutanol.     

Electrophoretic Studies on Plant Protoplasts I. pH Dependence of Zeta Potentials of Protoplasts from Various Sources

Electrophoretic mobilities of plant protoplasts from varioussources were measured, as a function of the pH of the medium,by a micro-electrophoresis technique to characterize the protoplastsin terms of curves of zeta potential vs. protoplast surfacepH (pH_s). The shape of the curves of zeta potential vs. pH_scurves differed among preparations of protoplasts isolated fromvarious species and strains. The isoelectric points (pI) ofthe protoplasts measured in this study were between 3.0 and4.0. These differences among the protoplasts suggest that itmay be possible to develop an electrophoretic method for theselection of protoplasts. The shape of the curves of zeta potentialvs. pH_s also indicated that carboxyl groups, as well as phosphategroups, may contribute to the negative charges on the surfaceof protoplasts. (Received October 14, 1988; Accepted February 22, 1989)     

2-(p-Nitrophenyl)-2''-deoxyadenosine, a new type of mutagenic nucleoside.

A crude preparation of 2-phenyladenosine was found to be mutagenic in the Ames Salmonella assay. In the purification of this preparation, it was revealed that 2-phenyladenosine itself was nonmutagenic but that 2-(m- and p-nitrophenyl)-adenosines (5m,p) contaminating the sample were the mutagenic principles. A structure-activity relationship study was carried out, and it was found that 5p, 2-(p-nitrophenyl)-adenine (7p), and 2-(p-nitrophenyl)-2'-deoxyadenosine (15p) were strongly mutagenic toward S. typhimurium TA98 and TA100 without metabolic activation, the potency being in the order 15p greater than 7p greater than 5p. The potency of 15p in TA98 was one order of magnitude greater than that of 4-nitroquinoline N-oxide. 15p also showed mutagenicity in the mouse cell line FM3A in culture.     

Triterpenes from Periandra dulcis roots

Three oleanane triterpenes were isolated from the roots of Periandra dulcis,and identified as 3β-hydroxy-25-al-olean-18-en-30-oic acid (periandric acid I), 3β-hydroxy-25-al-olean-12-en-30-oic acid (periandric acid II) and 3-oxo-25-hydroxy-olean-12-en-30-oic acid. The former two compounds (periandric acids I and II) were identical with the aglycones obtained by hydrolysis of periandrin I and II, respectively and the latter one was a new triterpene.     

Isolation of the Photoactive Reaction Center Complex that Contains Three Types of Fe-S Centers and a Cytochrome c Subunit from the Green Sulfur Bacterium Chlorobium limicola f. thiosulfatophilum, Strain Larsen

The photoactive reaction center (RC) complex from the greensulfur bacterium Chlorobium limicola f. thiosulfatophilum, strainLarsen, was isolated after solubilization and ammonium sulfatefractionation followed by ion-exchange chromatography. The spectrumof the complex was almost identical with that of the similarRC complex isolated by Feiler et al. [(1992) Biochemistry 31:2608–2614] except for the presence of cytochrome c₅₅₁instead of c₅₅₃ in the latter study. A molecular ratio of BChla to P840 of the isolated RC complex was assayed to be 25–35.SDSPAGE analysis revealed that the isolated complex containedthree major polypeptides with apparent molecular masses of 68,41 and 21 kDa, respectively. The 21-kDa polypeptide was identifiedto be a heme-binding protein by staining the gel for peroxidaseactivity. The cytochrome c₅₅₁ was oxidized by flash light ina biphasic manner with half times of 90 and 390 µs, respectively,that coincided with the reduction half times of P840⁺. Threedistinct iron-sulfur centers assigned to F_A, F_B and F_x, respectively,from their g-values were detected by EPR spectroscopy at cryogenictemperature. These results suggest that the present preparationcontains a minimal functional unit of the RC of this bacterium,and that this complex appears to lie on a evolutionary linebetween RC's of purple bacteria and photosystem I. (Received August 18, 1992; Accepted October 28, 1992)     

Inhibition of indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase by β-carboline and indole derivatives

β-Carboline derivatives inhibited both indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase activities from various sources. Among them, norharman is most potent for both enzymes from mammalian sources. Kinetic studies revealed that norharman is uncompetitive (K_i = 0.12 mm) with l-tryptophan for rabbit intestinal indoleamine 2,3-dioxygenase, and linearly competitive (K_i = 0.29 mm) with l-tryptophan for mouse liver tryptophan 2,3-dioxygenase. In addition, some β-carbolines selectively inhibited one enzyme or the other. Pseudomonad tryptophan 2,3-dioxygenase was inhibited by a different spectrum of β-carbolines. Such a selective inhibition by the structure of substrate analogs is more evident by the use of indole derivatives. Indole-3-acetamide, indole-3-acetonitrile and indole-3-acrylic acid exhibited a potent inhibition for mammalian tryptophan 2,3-dioxygenase, while they moderately inhibited the pseudomonad enzyme. However, they showed no inhibition for indoleamine 2,3-dioxygenase. These results suggest the difference of the structures of the active sites among these enzymes from various sources.     

Dehydrodieugenol and its monomethyl ether from Virola carinata

The constituents of Virola carinata were established as dehydrodieugenol, its monomethyl ether and sitosterol.     

A blue protein as an inactivating factor for nitrite reductase from Alcaligenes faecalis strain S-6

A blue protein with a molecule weight of 12,000 containing 1 atom of type I Cu2+ was purified and crystallized from a denitrifying bacterium, Alcaligenes faecalis strain S-6, as an inactivating factor for copper-containing nitrite reductase of the same organism. Inactivation of the enzyme occurred when the enzyme was incubated aerobically with a catalytic amount of the blue protein in the presence of reducing agents such as cysteine and ascorbate. The blue protein acts as a direct electron donor for the enzyme to catalyze the reduction of nitrite, but in the absence of nitrite, the enzyme-reduced blue protein system reacts with oxygen to produce H2O2. A suicide inactivation mechanism of the enzyme due to this H2O2 production is proposed.