Dielectric relaxation of DNA in aqueous solutions.

Using a four-electrode cell and a new electronic system for direct detection of the frequency differences specturm of solution impedance, the complex dielectric constant of calf thymus DNA (M_r = 4 × 10⁶) in aqueous NaCl at 10°C is measured at frequencies ranging from 0.2 Hz to 30 kHz. The DNA concentrations are C_p = 0.01% and 0.05%, and the NaCl concentrations are varied from C_s = 10^?4 M to 10^?3 M. A single relaxation regions is found in this frequency range, the relaxation frequency being 10 Hz at C_p = 0.01% and C_s = 10^?3 M. At C_p = 0.05% it is evidenced that the DNA chains have appreciable intermolecular interactions. The dielectric relaxaton time τ_d at C_p = 0.01% agrees well with the rotational relaxation time estimated from the reduced visocisty on the assumption that the DNA is not representable as a rigid rod but a coiled chain. It is concluded that the dielectric relaxiatioinis ascribed to the rotation of the molecule. Observed values of dielectric increment and other experimental findings are reasonably explained by assuming that the dipole moment of DNA results from the slow counterion fluctuation which has a longer relaxation time than τ_d.     

Qualitative abnormality of insulin secretion in a case with insulinoma.

We have presented here a case of atypical insulinoma. Despite the recurrent episodes of hypoglycemic symptoms, the plasma level of insulin has never been excessive at fasting or by regular provocative tests. Detailed examination had demonstrated qualitative abnormality of insulin secretion. Hyposuppressibility of insulin secretion by hypoglycemia, borderline diabetic curve of glucose tolerance test, blunted response ot insulin to glucagon and leucine were the principle characteristics of these abnormalities. After removal of adenoma, insulin response to glucose, glucagon and leucine was improved. Only secretion provoked a high level of insulin and this abnormal elevation was no longer seen after the removal of adenoma. A removed elevation was no longer seen after the removal of adenoma. A removed insulinoma contained 25 U of immunoreactive insulin per gram tissue, but was negative for aldehyde-fuchsin staining. On electromicroscopy only atypical beta-cell granules were seen.     

Isolation and characterization of different-sized nucleoli from Ehrlich ascites tumor cells : Evidence of different nucleolar ribosomal cistrons

A procedure was developed for isolation of variously sized nucleoli in order to study the mechanism of nucleolar formation from multiple nucleolar organizers and to compare the compositions of different-sized nucleoli from Ehrlich ascites tumor cells. Relatively small nucleoli and large nucleoli from Ehrlich ascites tumor cells were separated by centrifugation at 400 g for 5 min in a layer of 0.34 M sucrose over 0.88 M sucrose. Small nucleoli remained in the 0.34 M sucrose layer while the large nucleoli accumulated in the 0.88 M sucrose.Three fractions, provisionally named small, intermediate and large nucleoli, containing 0.33, 0.41 and 0.84 pg DNA/nucleolus, respectively, were separated. Unfractionated nucleoli contained 0.59 pg DNA/nucleolus. The RNA content also increased with the size of the nucleolus and no significant difference was observed in the RNA/DNA ratios in the three fractions. Large nucleoli incorporated more [³H]uridine and [³²P]orthophosphate into RNA than did small nucleoli, but the base compositions of the RNAs extracted from the different-sized nucleoli were similar. No significant fragmentation occurred on sonication of large nucleoli for 3 min, so the observed difference in the DNA contents was not due to mechanical damage of the nucleoli.The DNAs of these different-sized nucleoli were analysed on CsCl gradients. The nucleoli contained similar percentages of satellite DNA (20–22%) which were also similar to those of total, unfractionated nucleoli. Approx. 10% of the extranucleolar DNA is satellite DNA—thus the nucleolar fractions were probably not appreciably contaminated with extranucleolar DNA. The DNA of small nucleoli contained a slightly lower percentage (0.058%) of ribosomal cistrons than large nucleoli (0.081%). This means that the higher content of DNA in the large nucleoli is not merely due to longer sized chromatin with extra regions of the vicinity of nucleolar organizers. Thus these results suggest that the total content of ribosomal cistrons/nucleolus is roughly proportional to the DNA content of the nucleoli, at least in Ehrlich ascites tumor cells. Namely, the number of ribosomal cistrons per nucleolus for small, intermediate and large nucleoli is 40, 60 and 130, respectively.     

Radioimmunoassay for 11-deoxycortisol using iodine-labeled tracer.

A simple and sensitive radioimmunoassay for 11-deoxycortisol was developed. The antiserum produced in rabbits by immunizing with a complex of 11-deoxycortisol-3-oxime and bovine serum albumin (BSA) has little cross-reactivity with other endogenous steroids. The immunoassay procedure requires only one-step ethanol denaturation of binding proteins in plasma and extraction by an organic solvent can be omitted. Furthermore, use of 125I-labeled tracer significantly simplify the counting procedure. The method is sensitive enough to detect 1 microng/100 ml of 11-deoxycortisol. Plasma 11-deoxycortisol levels measured by this method after the administration of a single dose of metyrapone ranged from 5.0 to 19.2 microng/100 ml, whereas they were 0 to 4.0 microng/100 ml in hypopituitary patients. It is concluded that this simple method is useful for the routine assay of plasma 11-deoxycortisol as a parameter of the metyrapone tests.     

Effect of aluminum on iron-induced lipid peroxidation and protein oxidative modification of mouse brain homogenate

In the present study the authors report on the enhancing effect of aluminum(III) (Al[III]) on iron(II)(Fe[II])-induced lipid peroxidation (LPO) of mice brain homogenate, which occurs in a concentration and time-dependent manner. No evidence of LPO caused by Al alone was found. Both Al(III) and Fe(II) ions induced protein oxidative modifications in mice brain homogenate, in a time and concentrationdependent manner. Aluminum enhances Fe(II)-induced protein oxidative modification at a concentration of 2:1 and 1:1 Al:Fe molar ratios. However, Al suppress Fe(II)-induced protein oxidative modification at a concentration of 0.5:1 Al:Fe molar ratio. Addition of ethylenediaminetetraacetic acid (EDTA) inhibits both LPO and protein oxidative modifications induced by Al(III) and Fe(II) ions. Addition of mannitol and of Superoxide dismutase (SOD) did not show such effects. It is concluded that in mice brain homogenate, Al accelerates Fe(II)-induced LPO. Protein oxidative modifications caused by Fe(II) and/or Al ions are enhanced at high, but suppressed at low concentrations of Al ions. The latter observation suggests a possible biological role of Al as an antioxidant.     

Studies on chilling injury in plant cells II. Ultrastructural changes in cells rewarmed at 26?C after chilling treatment

Both the restoration and deterioration of ultrastructures wereobserved during therewarming of cultured cells of Cornus stoloniferain which chilling at 0?C had caused an apparent change in themorphology of the organelles. Complete restoration of the ultrastructures,moderately altered by the 12-hr chilling, took place within12 hr of wanning at 26?C. Even in cells chilled for 24 hr, severelyaltered ultrastructures were partially or completely repairedin more than fifty percent of the treated cells. Some cellschilled for 24 hr, however, displayed further deteriorationof their ultrastructures during rewarming. Restoration of therough endoplasmic reticulum and the development of polysomesin recovering cells were characteristic of the early stage ofrewarming. Rupture of the tonoplast was sometimes observed duringrewarming of cells chilled for 24 hr. A possible role for therough endoplasmic reticulum and for the integrity of the tonoplastin cell recovery during the chill-warm sequence is discussed. ¹Contribution No. 2026 from the Institute of Low TemperatureScience, Hokkaido University. ²This work was supported in part by Grant 248004 from the Ministryof Education. (Received November 6, 1978; )     

Phototropin‐ and photosynthesis‐dependent mitochondrial positioning in Arabidopsis thaliana mesophyll cells

Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic interactions. We previously reported that, in leaf palisade cells of Arabidopsis thaliana, mitochondria exhibit blue‐light‐dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue‐light receptor phototropins. In this study, precise motility analyses by fluorescent microscopy revealed that the individual mitochondria in palisade cells, labeled with green fluorescent protein, exhibit typical stop‐and‐go movement. When exposed to blue light, the velocity of moving mitochondria increased in 30 min, whereas after 4 h, the frequency of stoppage of mitochondrial movement markedly increased. Using different mutant plants, we concluded that the presence of both phototropin1 and phototropin2 is necessary for the early acceleration of mitochondrial movement. On the contrary, the late enhancement of stoppage of mitochondrial movement occurs only in the presence of phototropin2 and only when intact photosynthesis takes place. A plasma‐membrane ghost assay suggested that the stopped mitochondria are firmly adhered to chloroplasts. These results indicate that the physical interaction between mitochondria and chloroplasts is cooperatively mediated by phototropin2‐ and photosynthesis‐dependent signals. The present study might add novel regulatory mechanism for light‐dependent plant organelle interactions.     

The skull evolution of oviraptorosaurian dinosaurs: the role of niche partitioning in diversification

Oviraptorosaurs are bird‐like theropod dinosaurs that thrived in the final pre‐extinction ecosystems during the latest Cretaceous, and the beaked, toothless skulls of derived species are regarded as some of the most peculiar among dinosaurs. Their aberrant morphologies are hypothesized to have been caused by rapid evolution triggered by an ecological/biological driver, but little is known about how their skull shapes and functional abilities diversified. Here, we use quantitative techniques to study oviraptorosaur skull form and mandibular function. We demonstrate that the snout is particularly variable, that mandibular form and upper/lower beak form are significantly correlated with phylogeny, and that there is a strong and significant correlation between mandibular function and mandible/lower beak shape, suggesting a form–function association. The form–function relationship and phylogenetic signals, along with a moderate allometric signal in lower beak form, indicate that similar mechanisms governed beak shape in oviraptorosaurs and extant birds. The two derived oviraptorosaur clades, oviraptorids and caenagnathids, are significantly separated in morphospace and functional space, indicating that they partitioned niches. Oviraptorids coexisting in the same ecosystem are also widely spread in morphological and functional space, suggesting that they finely partitioned feeding niches, whereas caenagnathids exhibit extreme disparity in beak size. The diversity of skull form and function was likely key to the diversification and evolutionary success of oviraptorosaurs in the latest Cretaceous.