As part of an electrophoretic study on Isoëtes, a number of Neotropical and North American species were examined for allozyme variation in TPI. Three of these species—I. storkii, I. flaccida, and I. mexicana—exhibit three distinct zones of TPI activity. The two most anodally migrating zones are comparable to the two zones found in most angiosperms and in several other species of Isoëtes. The single or three-banded phenotypes produced at these loci correspond, respectively, to the homozygous and heterozygous patterns typical of a dimeric enzyme. The most cathodal zone (zone III) differs in producing either single or two-banded phenotypes. Analyses of these three zones indicate a nearly perfect correlation between zones II and III in putative allelic constitution and relative allelic mobility. Explanations involving TPI gene duplications and/or null alleles fail to account for the peculiar banding characteristics and origin of activity zone III. An alternative hypothesis involving a protease duplication and differential post-translational modification is postulated. This hypothesis adequately explains the zone III phenotypes and fixation of the third activity zone in the species examined. Amino acid sequencing is suggested as the most direct test of this hypothesis. The taxonomic distribution of TPI III generally supports a previous, morphologically-based, hypothesis on species relationships in Isoëtes. The presence of this zone is regarded as an independent synapomorphy for a major clade of Neotropical Isoëtes.相似文献
OBJECTIVES: To examine the relation between bed use, social deprivation, and overall bed availability in acute adult psychiatric units and to explore the range of alternative residential options. DESIGN: Cross sectional survey, combined with one day census data; ratings by and interviews with staff; examination of routine data sources. SETTINGS: Nationally representative sample of acute psychiatric units. SUBJECTS: 2236 patients who were inpatients on census day. MAIN OUTCOME MEASURES: Bed occupancy levels, judged need for continuing inpatient care, reasons preventing discharge, scores on the Health of the Nation outcome scales. RESULTS: Bed occupancy was related to social deprivation and total availability of acute beds (r = 0.66, 95% confidence interval 0.19 to 0.88, F = 8.72, df = 2.23; P = 0.002). However, 27% (603/2215) of current inpatients (61% (90/148) of those with stays of > 6 months) were judged not to need continuing admission. The major reasons preventing discharge were lack of suitable accommodation (37% (176/482) of patients in hospital < 6 months v 36% (31/86) of those in hospital > 6 months); inadequate domiciliary based community support (23% (113) v 9% (8)); and lack of long term rehabilitation places (21% (100) v 47% (40)). Scores on the Health of the Nation outcome scale were generally consistent with these staff judgments. CONCLUSIONS: The shortage of beds in acute psychiatric units is related to both social deprivation and the overall availability of acute beds. Patients currently inappropriately placed on acute admission wards should be relocated into more suitable accommodation, either in hospital or in the community. A range of provisions is required; simply providing more acute beds is not the answer. 相似文献
Heat evolved by isolated soybean (Glycine max cv Clark) nodules was measured to estimate more directly the metabolic cost associated with the symbiotic N2 fixation system. A calorimeter constructed by modifying standard laboratory equipment allowed measurement on 1 gram of detached nodules under a controlled gas stream. Simultaneous gas balance and heat output determinations were made.
There was major heat output by nodules for all of the nitrogenase substrates tested (H+, N2, N2O, and C2H2) further establishing the in vivo energy inefficiency of biological N2 fixation. Exposure to a short burst of 100% O2 partially inactivated nitrogenase to permit calculations of heat evolved per mole of substrate reduced. The specific rate of heat evolution for H+ reductions was 171 ± 6 kilocalories per mole H2 evolved in an Ar-O2 atmosphere, that for N2 fixation was 784 ± 26 kilocalories per mole H2 evolved and N2 fixed, and that for C2H2 reduction was 250 ± 12 kilocalories/mole C2H4 formed. When the appropriate thermodynamic parameters are taken into account for the different substrates and products, a ΔH′ of −200 kilocalories per mole 2e− is shown to be associated with active transfer of electrons by the nitrogenase system. These values lead to a calculated N2 fixation cost of 9.5 grams glucose per gram N2 fixed or 3.8 grams C per gram N2, which is in close agreement with earlier calculations based on nodular CO2 production.
Nuclei from frozen calf thymus suspended in buffer were analyzed for metal content prior to and after repeated washing. After three such extractions about 0.1 micrograms Zn/mg DNA and 0.025 micrograms Cu/mg DNA remained tightly associated with chromatin. This level of metal was essentially unchanged with subsequent washings. Digestion of extracted nuclei with micrococcal nuclease yielded soluble nucleoprotein containing zinc and copper. Metal enriched regions of chromatin appeared to be preferentially solubilized by digestion, and the solubilized metal was only partially dializable either with or without EDTA. Metal profiles generated from gel (A-5m) chromatography analysis of chelated and non-chelated solubilized chromatin were distinctive in that copper was undetectable (by flame AA) while zinc was associated only with low molecular weight products when EDTA was used. In contrast, both metals were detected with higher molecular weight oligonucleosomes in the absence of chelating agents. Additionally, the two metals localized within nucleoprotein peaks and these metal-containing regions were only resolved by gel chromatography when EDTA was omitted throughout the procedure. A discrete Cu-rich species in a region of the profile suggests a subset of Cu-rich nucleoprotein complexes. 相似文献