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2.
M A Porter S Milanez C D Stringer F C Hartman 《Archives of biochemistry and biophysics》1986,245(1):14-23
An efficient purification procedure utilizing affinity chromatography is described for spinach ribulose-5-phosphate kinase, a light-regulated chloroplastic enzyme. Gel filtration and polyacrylamide gel electrophoresis of the purified enzyme reveal a dimeric structure of 44,000 Mr subunits. Chemical crosslinking with dimethyl suberimidate confirms the presence of two subunits per molecule of native kinase, which are shown to be identical by partial NH2-terminal sequencing. Based on sulfhydryl titrations and on amino acid analyses, each subunit contains four to five cysteinyl residues. The observed slow loss of activity during spontaneous oxidation in air-saturated buffer correlates with the intramolecular oxidation of two sulfhydryl groups, presumably those involved in thioredoxin-mediated regulation. 相似文献
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P Raychaudhuri E A Stringer D M Valenzuela U Maitra 《The Journal of biological chemistry》1984,259(19):11930-11935
A ribosomal subunit antiassociation activity has been purified from both the postribosomal supernatant and ribosomal salt-wash protein fractions of rabbit reticulocyte lysates. A majority (greater than 90%) of the activity is associated with a low molecular weight protein of Mr of approximately 25,000. A small but significant level of antiassociation activity (less than 10%) was found to be associated with higher molecular weight protein fractions. The purified 25,000-dalton antiassociation factor interacts with 60 S ribosomal subunits to prevent them from reassociating with 40 S ribosomal subunits. The factor does not seem to interact directly with 40 S subunits nor does it dissociate 80 S monosomes. The properties of this factor are thus similar to the eukaryotic initiation factor 6 isolated from both wheat germ and calf liver extracts. 相似文献
5.
This study was designed to investigate the mitotic response to wounding in the rat thyroid. The spatial distribution of mitotic activity 48 hr after incision of the thyroid isthmus, or mere exposure of the gland (sham-operation), was assessed using a stathmokinetic technique. Incision resulted in a 66-fold increase over normal in metaphase index adjacent to the wound, falling over 2 mm to a stable 13-fold elevation. Sham-operation produced a smaller response with a complete return to normal levels over 1-1 X 5 mm. The results demonstrate that there is a dramatic localized mitotic response to wounding in the thyroid together with a smaller generalized response. Further, the response to sham-operation indicates that thyroid follicular cells respond to a diffusible 'wound hormone'. We suggest that this may be a major mechanism mediating reparative growth in this gland. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
9.
Refixation of xylem sap CO2 in Populus deltoides 总被引:1,自引:0,他引:1
Vascular plants have respiring tissues which are perfused by the transpiration stream, allowing solubilization of respiratory CO2 in the xylem sap. The transpiration stream could provide a conduit for the internal delivery of respiratory CO2 to leaves. Trees have large amounts of respiring tissues in the root systems and stems, and may have elevated levels of CO2 in the xylem sap which could be delivered to and refixed by the leaves. Xylem sap from the shoots of three Populus deltoides trees had mean dissolved inorganic carbon concentrations (CO2+H2CO3+HCO?3) ranging from 0. 5 to 0. 9 mM. When excised leaves were allowed to transpire 1 mM[14C]NaHCO3, 99. 6% of the label was fixed in the light. Seventy-seven percent of the label was fixed in major veins and the remainder was fixed in the minor veins. Autoradiography confirmed that label was confined to the vasculature. In the dark, approximately 80% of the transpired label escaped the leaf, the remainder was fixed in the major veins, slightly elevating dark respiration measurements. This indicates that the vascular tissue in P. deltoides leaves is supplied with a carbon source distinct from the atmospheric source fixed by interveinal lamina. However, the contribution of CO2 delivered to the leaves in the transpiration stream and fixed in the veins was only 0. 5% of atmospheric CO2 uptake. In the light 90% of the label was found in sugar, starch and protein, a pattern similar to that found for atmospheric uptake of[14C]CO2. Compared with leaves labelled in the light, leaves labelled in the dark had more label in organic acid, amino acid and protein and less label in sugar and starch. After a 5-s pulse the majority of the label fed to petioles in both the light and the dark was found in malate. The majority of the label was found in malate at 120 s in the dark; only 2% of the label was found in phosphorylated compounds at 120 s. The proportion of label found in phosphorylated compounds increased from 17% at 5 s to 80% at 120 s in the light. This suggests that CO2 delivered to leaves in the light via the transpiration stream is fixed in the veins, a small portion through dark fixation into malate, the remainder by C-3 photosynthesis. 相似文献
10.
Carolin Röding Chris Stringer Rodrigo S. Lacruz Katerina Harvati 《American journal of physical anthropology》2023,180(2):352-369