Ammonium uptake in Rhodopseudomonas capsulata

Investigations of the uptake of ammonium (NH ₄ ⁺ ) by Rhodopseudomonas capsulata B100 supported the presence of an NH ₄ ⁺ transport system. Experimentally NH ₄ ⁺ was determined by electrode or indophenol assay and saturation kinetics were observed with two apparent K _m's of 1.7 M and 11.1 M (pH 6.8, 30°) and a V _max at saturation of 50–60 nmol/min·mg protein. The optimum pH and temperature were 7.0 and 33° C, respectively. The Q₁₀ quotient was calculated to be 1.9 at 100 M NH ₄ ⁺ , indicating enzymatic involvement. In contrast to the wild type, B100, excretion of NH ₄ ⁺ , not uptake, was observed in a glutamine auxotroph, R. capsulata G29, which is derepressed for nitrogenase and lacks glutamine synthetase activity. G29R1, a revertant of G29, also took up NH ₄ ⁺ at the same rate as wild type and had fully restored glutamine synthetase activity. Partially restored derivatives, G29R5 and G29R6, grew more slowly than wild type on NH ₄ ⁺ as the nitrogen source, remained derepressed for nitrogenase in the presence of NH ₄ ⁺ , and displayed rates of NH ₄ ⁺ uptake in proportion to their glutamine synthetase activity. Ammonium uptake and glutamine synthetase activity were also restored in R. capsulata G29 exconjugants which had received the plasmid pPS25, containing the R. capsulata glutamine synthetase structural gene. These data suggest that NH ₄ ⁺ transport is tightly coupled to assimilation.Abbreviations used CHES cyclohexylaminoethanesulfonic acid - GS glutamine synthetase - SDS sodium dodecylsulfate     

Thiols and pancreatic beta-cell function: a review

In pancreatic islets insulin secretion in response to a variety of stimulators is sensitive to the redox state of extracellular and intracellular thiols. In this connection variations of plasma glutathione (GSH) may also be of importance. In the process of stimulus-secretion coupling, membrane thiols play an important role. One major localization of critical thiols appears to be related to the influx of calcium through the voltage-dependent channel. Other transmembranal ion movements and the cAMP system seem to be less sensitive to thiol oxidation than calcium influx via voltage-dependent Ca channels.     

Purification and properties of 1-phosphofructokinase from Escherichia coli

Abstract The thermophilic facultatively phototrophic green bacterium Chloroflexus aurantiacus strain Ok-70-fl was shown to possess sulfide-repressed hydrogenase activity. Biosynthesis of the enzyme was severely repressed by S²⁻ (5.7 mM) and stimulated specifically by Ni²⁺ and by molecular hydrogen. The hydrogenase was shown to be localized in the cytoplasmic membrane and could be solubilized from the latter by the detergent Triton X-100 in a state forming one enzymatically active band ( M _r 170 × 10³) in polyacrylamide gels. In the membraneous state, the hydrogenase had its maximal activity at 73°C and was active with methyl viologen, methylene blue, menadione and flavins, but not with NAD or NADP as electron acceptors. Solubilization of the enzyme with Triton X-100 resulted in a drastic increase in the FAD/FMN-linked activity.     

Heterologous hybridization of Azospirillum DNA to Rhizobium nod and fix genes

Abstract Probes containing the nod and hsn regions of Rhizobium meliloti and the fixABC genes of Rhizobium japonicum were used to perform hybridization experiments with endonuclease-restricted DNA from Azospirillum brasilense strains and 2 Azospirillum lipoferum strains. Homology to nod, hsn and fixA was found in the 4 Azospirillum strains.     

Effects of phosphorus and nitrogen enrichment on the phytoplankton in a tropical reservoir (Lobo Reservoir,Brazil)

The effects of enrichment with phosphate (0–500 µg. 1^–1) and forms of nitrogen (nitrate, nitrite, ammonia an and urea) (0–3500 µgg. ^–1) on the phytoplankton growth of Lobo Reservoir (Brazil) were studied in July, 1979. Suspended matter, chlorophyll a, cell concentrations and the carotenoid:cchlorophyll ratio were estimated following 14 days of in situ incubation. Phosphate alone caused no significant effects, but enrichment with nitrogen caused a substantial increase on the growth of phytoplankton. Comparison between the different forms of nitrogen showed insignificant effects after their additions with 350 µg. ^–1 and in combination with phosphate. However, when nitrogen was added in large quantities (3 500 µg. ^–1), significant differences between the nitrogeneous forms were found, with urea causing the strongest effect. In July, nitrogen is mhe main limiting nutrient to phytoplankton growth of Lobo Reservoir.Supported by CNPq and FAPESP.     

Effect of nonanoic acid and other short chain fatty acids on exchange properties in embryonic axes of Cicer arietinum during germination

Nonanoic acid, which inhibits germination in several seeds, enhanced ion efflux from embryonic axes of Cicer arietinum L., especially at temperatures above 25°C. Other short chain fatty acids had little effect on germination and ion leakage. Nonanoic acid also decreased uptake of ⁸⁶Rb⁺ and ²²Na⁺ and increased efflux of both isotopes from the embryonic axes into the incubation solution. Fusicoccin, which stimulates early germination in C. arietinum , counteracted the effects of nonanoic acid at both 25 and 30°C. These results suggest that nonanoic acid affects the integrity of plasmalemma and other membrane systems. Nonanoic acid thus inhibits cell elongation during early germination by disturbing ion exchange and inhibiting water uptake.     

Possible evidence for novel metabolism of nitrogen gas by a green alga

We report the isolation of a cukaryotic green alga ( Chlorella , strain WPI-2) which accumulates large stores of nitrogen (N) during growth in N-free medium and seems to incorporate¹⁴N₂, yet does not reduce acetylene to ethylene. Total N accumulation during growth on N-free medium and in gases free of combined N was measured by three methods: Kjeldahl, oxidative pyrolysis via chemiluminescence (Antek N analyzer), and Dumas (Coleman N analyzer). Increases in N ranging from 22–64%± 1% were observed. Isotope dilution studies using cells labelled with ¹⁵NO ₃- and then shifted to ¹⁴N₂ in N-free medium showed dilution of the ¹⁵N isotope by ¹⁴N from 5.67 to 5.32%± 0.05%. Using a variety of conditions, we were unable to demonstrate the reduction of acctylene to ethylene by WPI-2, although diazotrophic cyanobacteria gave positive results. Although the data on WPI-2 are not conclusive in establishing this alga as a diazotroph, the data do suggest that within the Chlorophyceae there may exist a novel form of nitrogen gas metabolism.