Some citrus chitinases also possess chitosanase activities

Several acidic chitinase and chitosanase isoforms were found in 4-week-old nonembryogenic sweet orange (Valencia [Citrus sinensis (L.) Osbeck]) callus tissue. Two isoforms (designated A1-CF1 and A1-CF2) were purified to homogeneity using HPLC size exclusion, anion exchange, and chromatofocusing techniques. Both hydrolase isoforms exhibited activity with either colloidal chitin or solubilized shrimp shell chitosan. Specific activities for the purified isoforms could not be calculated because of the lack of protein and contamination of ampholytes. However, the specific activities for chitinase and chitosanase after anion exchange were respectively 404 nmol GlcNAc per min per mg protein and 2,475 nmol GlcN per min per mg protein. The M_r for both enzymes was 30,500. The homogeneous proteins cross-reacted in western blots with antiserum against a basic class I potato leaf chitinase.     

What distinguishes cosmopolitan and endemicDrosophila species?

Summary CosmopolitanDrosophila species can survive wide ecological tolerances measured by resistance to desiccation/temperature extremes compared with endemic rain forest species. This, rather than any genetic features, is important in helping to explain the widespread distributions of cosmopolitan species.We thank Dr Lee Ehrman for cultures ofD. paulistorum, and the Australian Research Grants Committee for financial support.     

Assessing the impact of population stratification on genetic association studies

Population stratification refers to differences in allele frequencies between cases and controls due to systematic differences in ancestry rather than association of genes with disease. It has been proposed that false positive associations due to stratification can be controlled by genotyping a few dozen unlinked genetic markers. To assess stratification empirically, we analyzed data from 11 case-control and case-cohort association studies. We did not detect statistically significant evidence for stratification but did observe that assessments based on a few dozen markers lack power to rule out moderate levels of stratification that could cause false positive associations in studies designed to detect modest genetic risk factors. After increasing the number of markers and samples in a case-cohort study (the design most immune to stratification), we found that stratification was in fact present. Our results suggest that modest amounts of stratification can exist even in well designed studies.     

Direct addition of insulin inhibits a high affinity Ca2+-ATPase in isolated adipocyte plasma membranes.

The mechanism by which insulin regulates cellular metabolism remains unknown although indirect evidence suggests that alterations in intracellular calcium are important. More specifically, it has been proposed that insulin triggers an increase in intracellular calcium which is responsible for the subsequent modification of metabolic activities. The cell maintains a large electrochemical gradient for ionised calcium between the cytoplasm (less than 10(-6) M, as determined for muscle and nerve) and the extracellular environment (less than 10(-3) M). The plasma membrane may, therefore, be important in the regulation of calcium homeostasis, as a slight alteration in the processes maintaining this gradient could result in marked changes in cytoplasmic calcium. One such process is the active extrusion of calcium from the cell by a high affinity calcium-stimulated ATPase (Ca2+-ATPase). Such a mechanism has been well established in red cells and is postulated in nerve, liver and muscle. We have identified a high affinity Ca2+-ATPase in a plasma membrane-enriched subcellular fraction isolated from rat adipocytes which may provide the enzymatic basis for a calcium extrusion pump. We demonstrate here that the Ca2+-ATPase is specifically inhibited by the direct addition of physiological concentrations of insulin to the direct addition of physiological concentrations of insulin to the isolated plasma membranes. This effect suggests that direct regulation of calcium homeostasis may represent an important event in the mechanism of action of insulin.     

Enhancements of energetic particles near the heliospheric termination shock

The spacecraft Voyager 1 is at a distance greater than 85 au from the Sun, in the vicinity of the termination shock that marks the abrupt slowing of the supersonic solar wind and the beginning of the extended and unexplored distant heliosphere. This shock is expected to accelerate 'anomalous cosmic rays', as well as to re-accelerate Galactic cosmic rays and low-energy particles from the inner Solar System. Here we report a significant increase in the numbers of energetic ions and electrons that persisted for seven months beginning in mid-2002. This increase differs from any previously observed in that there was a simultaneous increase in Galactic cosmic ray ions and electrons, anomalous cosmic rays and low-energy ions. The low-intensity level and spectral energy distribution of the anomalous cosmic rays, however, indicates that Voyager 1 still has not reached the termination shock. Rather, the observed increase is an expected precursor event. We argue that the radial anisotropy of the cosmic rays is expected to be small in the foreshock region, as is observed.     

In vitro reactivation of anaphase spindle elongation using isolated diatom spindles

A key step for analysing the mechanochemistry of mitosis would be the isolation of a functional spindle capable of anaphase chromosome movement in vitro. Although Mazia and Dan first isolated spindles in 1952, with one or two possible exceptions, isolated spindles are non-functional. An alternative approach has used permeabilized cells to study anaphase chromosome movement, but these preparations are biochemically and morphologically complex, and hence difficult to analyse. We describe here a simple procedure for isolating diatom spindles which are capable of anaphase spindle elongation in vitro. With addition of ATP, the two half-spindles slide completely apart, with concomitant decrease in the zone of overlap. Electron microscopy reveals decreased numbers of microtubules throughout the spindle after ATP addition and confirms the complete absence of structures beyond the spindle poles. These results are inconsistent with theoretical models of mitosis which suggest that spindle poles are pushed apart by microtubule growth, are pulled apart by external forces applied to the poles, or are released from tension generated during spindle formation. The results are consitent with models that postulate mechanical interactions in the zone of microtubule overlap as a factor in spindle elongation.     

An index of goodness-of-fit based on noncentrality

Akaike's Information Criterion is systematically dependent on sample size, and therefore cannot be used in practice as a basis for model selection. An alternative measure of goodness-of-fit, based like Akaike's on the noncentrality parameter, appears to be consistent over variations in sample size.