Impacts of management practices on bioenergy feedstock yield and economic feasibility on Conservation Reserve Program grasslands

Perennial grass mixtures planted on Conservation Reserve Program (CRP) land are a potential source of dedicated bioenergy feedstock. Long‐term nitrogen (N) and harvest management are critical factors for maximizing biomass yield while maintaining the longevity of grass stands. A six‐year farm‐scale study was conducted to understand the impact of weather variability on biomass yield, determine optimal N fertilization and harvest timing management practices for sustainable biomass production, and estimate economic viability at six CRP sites in the United States. Precipitation during the growing season was a critical factor for annual biomass production across all regions, and annual biomass production was severely reduced when growing season precipitation was below 50% of average. The N rate of 112 kg ha^?1 produced the highest biomass yield at each location. Harvest timing resulting in the highest biomass yield was site‐specific and was a factor of predominant grass type, seasonal precipitation, and the number of harvests taken per year. The use of N fertilizer for yield enhancement unambiguously increased the cost of biomass regardless of the harvest timing for all six sites. The breakeven price of biomass at the farmgate ranged from $37 to $311 Mg^?1 depending on the rate of N application, timing of harvesting, and location when foregone opportunity costs were not considered. Breakeven prices ranged from $69 to $526 Mg^?1 when the loss of CRP land rental payments was included as an opportunity cost. Annual cost of the CRP to the federal government could be reduced by over 8% in the states included in this study; however, this would require the biomass price to be much higher than in the case where the landowner receives the CRP land rent. This field research demonstrated the importance of long‐term, farm‐scale research for accurate estimation of biomass feedstock production and economic viability from perennial grasslands.     

Regulation ofEscherichia coli catalases by anaerobiosis and catabolite repression

Escherichia coli has two forms of catalases, HPI and HPII. Both enzymes, but mainly HPII, are induced in cells reaching the stationary growth phase or under anaerobic conditions and are repressed in the presence of glucose. The induction at the stationary phase is dependent onfnr, a gene that regulates the expression of anaerobically induced proteins. The inhibition by glucose is not affected by cyclic AMP (cAMP) but is reduced in acrp mutant. The results show that HPII belongs to the group of genes controlled by the Fnr protein and is catabolically repressed in a manner that is independent of cAMP.     

Effect of Adenosine and Deoxyadenosine on the Incorporation and Breakdown of Thymidine in Escherichia coli K-12

Deoxyadenosine (AdR) and adenosine (AR) enhance the incorporation of thymidine (TdR) into bacterial deoxyribonucleic acid (DNA) by the inhibition of TdR phosphorolysis in vivo. Neither of the purine nucleosides has an effect on the reaction catalyzed by TdR phosphorylase in vitro. AdR induces TdR phosphorylase and both purine nucleosides induce purine nucleoside phosphorylase. AR can stimulate uptake of more TdR into bacterial DNA than AdR.     

Bacterial Conjugation: An Analysis of Mixed Recombinant Clones

A fraction of recombinant colonies resulting from conjugation is heterogenetic for unselected markers. Constitutivity for alkaline phosphatase synthesis (phoR) is studied as the unselected marker. The frequency of phoR heterogeneity depends on the genetic distance between phoR and the selected marker. Various models are considered which explain the formation of heterogenetic colonies (mixed clones), and experiments are described which test these models. It is concluded that the Hfr fragment can replicate and participate more than once in recombination thus yielding heterogenetic colonies.     

Phosphorolysis of 5-Fluoro-2′-Deoxyuridine in Escherichia coli and Its Inhibition by Nucleosides

The effect of ribonucleosides and deoxyribonucleosides on the phosphorolysis of 5-fluoro-2'-deoxyuridine (FUdR) was examined in cells of Escherichia coli. All nucleosides tested except guanosine and deoxyguanosine inhibited phosphorolysis. By using genetically marked strains it was found that in vivo FUdR is a specific substrate of thymidine phosphorylase.     

Biliary and urinary excretion of peptide leukotrienes in the domestic pig

The metabolism of leukotriene (LT)C4 and its major routes of elimination in vivo have been studied in four anesthetized domestic pigs administered intravenous [3H]-LTC4 (0.5 microCi/kg). The kinetic profile of LTC4 in the blood was followed for 60 min after administration while the biliary and urinary excretion of LTC4 and its metabolites were determined over a 120 min interval. The total recovery of radioactivity in bile and urine was 45% +/- 1 (n = 3) and 18% (n = 2) respectively. Examination of the radioactive metabolites in bile showed LTD4 (44% of biliary content) and LTE4 (21% of biliary content) as the major identified lipoxygenase products at t 1/2 (27 min). The only identified cysteinyl leukotriene observed in the urine was LTE4 (13% of urinary content). In both bile and urine substantial amounts of radioactivity were detected at the solvent front of the reverse phase chromatographic system indicating the presence of additional unidentified metabolites. We suggest that measurement of metabolites using these sampling methods may be useful for the detection and measurement of peptide leukotriene production in vivo.     

Influence of uracil photohydrate formation on the conformational properties of heterodinucleoside monophosphates

The structural properties of uracil photohydrates at the monomer and dimer level in aqueous solution have been examined in detail by nmr spectroscopy. Based on such evidence, the absolute configurations of the two possible diastereomers have been assigned, and the conformational perturbations induced by photohydration have been evaluated. In all instances, photohydration shifts the ²E ? ³E puckering equilibrium of the sugar ring of the uridylyl fragment towards ²E (from 12–18%). In addition, for both dimers examined in detail, ho⁶UpA and Apho⁶hU, the effect of dimerization on sugar pucker is such that the 3′-terminal unit shows a clear increase in the percentage of ³E (relative to the appropriate 5′-mononucleotide), whereas the percentage ³E of the 5′-terminal unit shows no change. This is contrary to the findings in the normal dinucleoside monophosphates, where an increased preference for ³E pucker occurs in both residues on dimerization and increased base stacking. Significant base–base interactions were observed in both hydrated dimers despite the loss of the planar π-system in the uracil fragment. In addition, the rate of photohydration for a particular dimer pair (e.g., ApU and UpA or GpU and UpG) is shown to be inversely dependent on the amount of base stacking in the parent dimer. This latter parameter has also been correlated with the ratio of the two possible diastereomers formed in the reaction and is associated with a preferential attack at one face of the pyrimidine base ring. The shift of the sugar puckering equilibrium towards ²E has been compared with similar shifts observed when adenosine and guanosine are methylated at N(1) and N(7), respectively. The possible biological significance of the above-mentioned conformational aspects is discussed.     

Mechanism of desensitization of adenylate cyclase in lutropin. GTP-dependent uncoupling of the receptor

Lutropin-sensitive adenylate cyclase ((EC 4.6.1.1) ATP pyrophosphate-lyase (cyclizing)) in purified rat ovarian plasma membranes is stimulated by lutropin 2- to 3-fold in the absence, but 15- to 20-fold in the presence of GTP or p(NH)ppG. Following 10 to 15 min of incubation at 30 degrees C in the presence of lutropin, enzyme activity declined (50%) in the presence of GTP but not in the presence of p(NH)ppG. This desensitizing process induced by lutropin and GTP is not seen if NaF is also included in the incubation medium. The desensitized state of the enzyme persists at 4 degrees C in membranes washed free of the incubation medium. In this state the enzyme is characterized by: (i) a reduced response to lutropin even in the presence of p(NH)ppG; (ii) its response to NaF is not different from that of untreated enzyme; (iii) it reconverts to a fully responsive state following incubation (10 min, 30 degrees C) in GTP-free medium, a process accelerated by p(NH)ppG; (iv) the receptor content as well as the stability of the receptor.hormone complex does not differ from that of untreated fully responsive enzyme. It is proposed that desensitization results from a GTP-dependent, hormone-stimulated reaction that leads to impaired coupling of the enzyme system. The desensitized state induced is transient and may revert to a responsive one under specified conditions.