Minimization of a sodium dithionite-derived interference in nitrate reductase-methyl viologen reactions

The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCL content of the sulfanilamide reagent.     

Melting of short DNA fragments. Relation between the nucleation constant of a spiral region and the ionic strength

Melting of two DNA duplexes of known nucleotide sequences containing 14 and 36 base pairs has been investigated within the range of ionic strength from 0.2 to 0.02 M [Na+]. The values of melting enthalpy of base pair delta H were measured for the duplex of 14 base pairs in the solutions of varying ionic strength. The values of delta H were obtained from slopes of linear plots of reciprocal melting temperature versus logarithm of oligonucleotide chains concentration. In the aforementioned range the decrease of the ionic strength causes a 5% decrease of delta H. By fitting the theoretical profiles to the experimental ones the ionic strength dependence of the nucleation constant beta was measured for DNA fragments of various lengths. With the decrease of the ionic strength the value of beta drops 2 times for the short duplex and 8 times for the long one.     

Single and dual task gait training in people with Parkinson's Disease: A protocol for a randomised controlled trial

Background  

Difficulty performing more than one task at a time (dual tasking) is a common and disabling problem experienced by people with Parkinson disease (PD). If asked to perform another task when walking, people with PD often take shorter steps or walk more slowly. Currently there is uncertainty about whether clinicians should teach people with PD to avoid dual tasking or whether they should encourage them to practice dual tasking with the hope that practice will lead to enhanced performance. This study will address this issue by comparing single to dual task gait training.     

Effects of Chromium(III) Picolinate on Cortisol and DHEAs Secretion in H295R Human Adrenocortical Cells

Dietary chromium(III) picolinate (CrPic) effects on circulating steroid hormones have been reported in various experimental animals. However, direct effects of CrPic on adrenocortical steroidogenesis are uncertain. Therefore, the objective was to determine the effects of CrPic on cortisol and dehydroepiandrosterone sulfate (DHEAs) secretion from H295R cells. In experiment 1, a 24-h exposure to CrPic (0 to 200 μM) had both linear (p < 0.001) and quadratic (p < 0.001) effects on cortisol secretion from forskolin-stimulated cells with the highest cortisol secretion at 0.1 μM of CrPic and the lowest at 200 μM of CrPic. In experiment 2, a 48-h exposure to CrPic (200 μM) decreased cortisol (p < 0.07) release from forskolin-stimulated cells during a 24-h collection period. In experiment 3, a 48-h exposure to CrPic (100 μM) decreased cortisol (p < 0.05) and DHEAs (p < 0.01) from forskolin-stimulated cells during a 24-h sampling period. In experiment 4, a 24-h exposure to forskolin followed by a 24-h exposure to both forskolin and CrPic (100 and 200 μM) decreased both cortisol and DHEAs secretion (p < 0.01). This study suggests that at high concentrations, CrPic inhibits aspects of steroidogenesis in agonist-stimulated adrenocortical cells.     

Purification of a prenyltransferase that elongates cis-polyisoprene rubber from the latex of Hevea brasiliensis

We have purified "rubber transferase" from latex of the commercial rubber tree Hevea brasiliensis and find that it is a dimer with a monomeric molecular mass of 38,000 Da, requires Mg2+, and is stabilized by thiols in agreement with studies of a partially purified preparation previously described (Archer, B. L., and Cockbain, E. G. (1969) Methods Enzymol. 15, 476-480). Greater than 90% of the [1-14C]isopentenyl pyrophosphate which is incorporated into deproteinated rubber particles by the purified prenyltransferase is added to high molecular mass polyisoprene (greater than 20,000 Da). Purified prenyltransferase and deproteinated rubber particles reconstitute 40-60% of the biosynthetic activity of whole latex in samples matched for rubber content. Incorporation is linear with added rubber particles up to at least 10 mg/ml rubber or 20 microM rubber molecules (based on a number average molecular mass of 500,000 Da). Prenyltransferase concentrations estimated in whole latex (0.37% or 160 nM) are sufficient to saturate all elongation sites in whole latex, and addition of purified prenyltransferase does not increase [1-14C]isopentenyl pyrophosphate incorporation. Deproteinated rubber particles can be titrated with the pure enzyme (Kd = 9 nM) demonstrating that the fraction of rubber molecules available for addition is low (approximately 0.01%). An estimated 7,000 isoprene units are added per complex at a rate of 1/s in a typical assay. Hevea prenyltransferase catalyzes the formation of cis-isoprene in the presence of rubber particles. However, in the absence of rubber particles and in the presence of dimethylallyl pyrophosphate, the purified prenyltransferase catalyzes the formation of geranyl pyrophosphate and all trans-farnesyl pyrophosphate as demonstrated by thin layer chromatography, gas chromatography, and molecular exclusion chromatography.     

Dipyridamole is neuroprotective for cultured rat embryonic cortical neurons

The effects of a clinically useful cardiovascular agent, dipyridamole, were examined in a rodent tissue culture model of neuroprotection. Dipyridamole effectively protected rat embryonic day 18 (E18) cortical neurons from either 48 h trophic deprivation or 48 h exposure to the glutathione synthesis inhibitor, L-buthionine (R,S) sulfoximine. The neuron sparing actions of dipyridamole were time- and concentration-dependent and mimicked the actions of exogenously applied glutathione. These results demonstrate that dipyridamole protects primary neuronal cultures against either trophic or chemically mediated insults, and suggest that dipyridamole has a potent antioxidant ability that compensates for glutathione depletion in neuronal cultures.     

A review of WHO International Standards for botulinum antitoxins.

Clostridium botulinum produces the most potent known toxins, with seven distinct serotypes currently defined (A-G). These toxins can cause a life threatening systemic toxicity whether through natural causes such as food poisoning, infant botulism, wound botulism, or through use as bio-terror agents (e.g. inhalational botulism). It was realised early on that standard reference botulinum antitoxins were required to reduce the variation between assays and ensure a consistent potency of therapeutic antitoxins and vaccines, and to define the serotype. This led to the International Unit being defined by the World Health Organisation (WHO) in the 1960s with the establishment of the first International Standards (IS) for serotypes A-F. Since then botulinum antitoxin ISs have been used world wide as the 'yard stick' to measure the neutralising potency of antitoxins. These primary WHO ISs are used to calibrate in house working reagents that are more extensively utilised. A definition of the International Unit for serotype G antitoxin has yet to be defined or accepted by the WHO and urgently needs addressing. However, before September 11th 2001 there was very little interest in botulinum antitoxin IS and as a result stocks of most of the original preparations are now completely exhausted or depleted and replacements long overdue. We have reviewed the extensive history and availability of the primary WHO ISs and interim materials. All type A and B antitoxin materials were recently assayed and their relative activities confirmed against the original IS preparations. The recent increase in demand for these materials has further exacerbated the shortage. We describe here the production and characterization of stable freeze dried potential candidate replacements along with a new prospective first IS for type G antitoxin. Available toxin A reference preparations are also briefly reviewed.     

Molecular characterization of germline NF2 gene rearrangements

Neurofibromatosis type 2 (NF2) is an autosomal dominant disease that causes a predisposition to nervous system tumors. Deleterious point mutations have been found in about 55% of NF2 patients, and large genomic deletions account for approximately 33% of NF2 gene alterations. The majority of these deletions are larger than 50 kb, with a breakpoint usually lying outside the NF2 gene. We identified two cases of intragenic deletion with loss of 1.5 and 40 kb, respectively. In both cases, one boundary of the deletion was located in or at the proximity of an SVA sequence in NF2 intron 4. No sequence identity longer than 5 bases and no signal of specific recombination have been evidenced on either side of the deletion breakpoints. These observations are compatible with a nonhomologous recombination being responsible for the genomic deletions. In a third case, a paracentric inversion of chromosome 22 was found. This chromosomal rearrangement breaks the NF2 gene in two parts and carries the first NF2 exon in a juxta-centromeric position. The variability in position of the deletions and the observation of a new chromosomal rearrangement in the NF2 gene underscore the importance of FISH analysis in the molecular diagnosis of NF2.