Defoliation-induced enhancement of total aboveground nitrogen yield of grasses

We conducted an experiment in a northern mixed-grass prairie at Wind Cave National Park, South Dakota, USA to evaluate the effect of defoliation frequency on aboveground net primary production (ANPP), shoot nitrogen concentration, and aboveground N yield of graminoids. ANPP was significantly reduced at weekly and biweekly defoliation frequencies, but unaffected relative to unclipped controls at monthly and bimonthly frequencies. By contrast, clipping at all frequencies increased shoot N concentration above that of controls, and this increase was greatest at monthly or more frequent defoliations. Total aboveground N yield and potential N yield to grazers were greatest at intermediate (bimonthly to biweekly) frequencies. We suggest that grazers may maximize their nutritional status in this system by periodically regrazing areas at frequencies near the approximately monthly optimum that we observed.     

The catalytic activities of DNA topoisomerase II are most closely associated with the DNA cleavage/religation steps.

DNA topoisomerase II regulates the three-dimensional organisation of DNA and is the principal target of many important anticancer and antimicrobial agents. These drugs usually act on the DNA cleavage/religation steps of the catalytic cycle resulting in accumulation of covalent DNA-topoisomerase II complexes. We have studied the different steps of the catalytic cycle as a function of salt concentration, which is a classical way to evaluate the biochemical properties of proteins. The results show that the catalytic activity of topoisomerase II follows a bell-shaped curve with optimum between 100 and 225 mM KCl. No straight-forward correlation exists between DNA binding and catalytic activity. The highest levels of drug-induced covalent DNA-topoisomerase II complexes are observed between 100 and 150 mM KCl. Remarkably, at salt concentrations between 150 mM and 225 mM KCl, topoisomerase II is converted into a drug-resistant form with greatly reduced levels of drug-induced DNA-topoisomerase II complexes. This is due to efficient religation rather than to absence of DNA cleavage as witnessed by relaxation of the supercoiled DNA substrate. In the absence of DNA, ATP hydrolysis is strongest at low salt concentrations. Unexpectedly, the addition of DNA stimulates ATP hydrolysis at 100 and 150 mM KCl, but has little or no effect below 100 mM KCl in spite of strong non-covalent DNA binding at these salt concentrations. Therefore, DNA-stimulated ATP hydrolysis appears to be associated with covalent rather than non-covalent binding of DNA to topoisomerase II. Taken together, the results suggest that it is the DNA cleavage/religation steps that are most closely associated with the catalytic activities of topoisomerase II providing a unifying theme for the biological and pharmacological modulation of this enzyme.     

Biopolymer of alginate nature with a predominance of L-guluronic acid

Highly viscous polysaccharide (250–350 kDa) of an alginate nature with a predominance of α-L-guluronic acid (M/G = 0.22) was obtained from Azotobacter vinelandi. The yield of polysaccharide was 20.5 ± 0.5 g/l when cultured in a medium containing molasses at a viscosity of the cultural liquid of over 30000 cSt. The biopolymer is stable at pH 4.0–9.0 in a wide temperature range and well soluble in highly mineralized water; it retains a high viscosity level and can be used in the petroleum industry for enhanced oil recovery.     

Fragment of the gene encoding chymotrypsin and trypsin inhibitor protein of potato tubers

Product of polymerase chain reaction designated as PKPIJ-B was isolated after amplification from genomic DNA of potato (Solarium tuberosum L., Zhukov Jubilee cultivar) using the designed primers. Nucleotide sequence of PKPIJ-B was determined and amino acid sequence of protein was restored. Analysis of this sequence has allowed us to suggest that isolated gene fragment encodes chymotrypsin and trypsin inhibitor protein (PKCI-23 potato Kunitz-type chymotrypsin inhibitor) of potato tubers.     

D-glucosamine propanedithioacetal, an efficient chiral auxiliary in beta-lactam chemistry.

The synthesis of some monocyclic beta-lactams (monobactams) by the Staudinger reaction using D-glucosamine propanedithioacetal as chiral auxiliary is reported. The influence of several radicals at C3, C4, and C1' (sugar moiety) as well as other structural aspects are considered in relation to the antielastase activity.