Pulmonary gas exchange in Andean natives with excessive polycythemia--effect of hemodilution

Pulmonary gas exchange in Andean natives (n = 8) with excessive high-altitude (3,600-4,200 m) polycythemia (hematocrit 65.1 +/- 6.6%) and hypoxemia (arterial PO2 45.6 +/- 5.6 Torr) in the absence of pulmonary or cardiovascular disease was investigated both before and after isovolemic hemodilution by use of the inert gas elimination technique. The investigations were carried out in La Paz, Bolivia (3,650 m, 500 mmHg barometric pressure). Before hemodilution, a low ventilation-perfusion (VA/Q) mode (VA/Q less than 0.1) without true shunt accounted for 11.6 +/- 5.5% of the total blood flow and was mainly responsible for the hypoxemia. The hypoventilation with a low mixed venous PO2 value may have contributed to the observed hypoxemia in the absence of an impairment in alveolar capillary diffusion. After hemodilution, cardiac output and ventilation increased from 5.5 +/- 1.2 to 6.9 +/- 1.2 l/min and from 8.5 +/- 1.4 to 9.6 +/- 1.3 l/min, respectively, although arterial and venous PO2 remained constant. VA/Q mismatching fell slightly but significantly. The hypoxemia observed in subjects suffering from high-altitude excessive polycythemia was attributed to an increased in blood flow perfusing poorly ventilated areas, but without true intra- or extrapulmonary shunt. Hypoventilation as well as a low mixed venous PO2 value may also have contributed to the observed hypoxemia.     

The hedgehog uterus. A comparative transmission electron-microscopic study

The ultrastructure of the luminal epithelium of the hedgehog uterus is described on the basis of material taken from 11 animals in three different hormonal situations: castrated, active and hibernating animals. The whole uterine epithelium is composed of microvillous cells. Its appearance is very similar in ovariectomized and hibernating animals. It differs from that observed in active animals where the epithelium is taller, microvilli are more numerous and longer, and where nuclei and cytoplasm display a very active ultrastructural appearance. The results now available indicate that ultrastructural changes occurring within the cells are certainly correlated with plasma sex steroid hormone concentrations. The present paper also reports the regular occurrence of nuclear bodies in uterine cells.     

Association-dependent active folding of alpha and beta subunits of lutropin (luteinizing hormone).

The kinetics of the structural transition of ovine lutropin (luteinizing hormone) from a dissociated and partially unfolded state to a biologically active, folded and associated state were studied from pH 1.8 to 6.5 by difference spectroscopy, circular dichroism, light scattering and ultracentrifugation under various conditions of temperature and ionic strength. Between pH 2.8 and 5.3 there is a thermodynamically reversible equilibrium between the two states of the hormone with a half-transition pH of 4.3 ± 0.1 at 26 °C. The interconversion of native folding to dissociated state is strictly first-order, and most of the kinetic results can be described in terms of two exponential decays with lifetimes of 20 and 100 seconds at pH 2 and 26 °C with one intermediate. A second intermediate with a short lifetime (1.5 s) is detected with stopped-flow experiments; its spectroscopic contribution is small. Refolding from the dissociated state is always second-order in the concentration range studied (12 to 110 μm lutropin), with rates at 26 °C, 1.4 m⁻¹ s⁻¹ at pH 4.3 and 2.2 m⁻¹ s⁻¹ at pH 5.3. The temperature dependence of the rate constant of active folding at pH 5.3 corresponds to activation parameters $\text{ΔH}{}^1\text{= +23.5}\text{kcal mol}{}^{\mathrm{-1}}\text{and}\text{ΔS}{}^1\text{= +21.6}\text{cal deg}{}^{\mathrm{-1}}$ mol⁻¹.From these data and computer-simulation studies, a simplest possible mechanism is proposed that involves the formation of a loose complex between the α and β subunits of the hormone, followed by a slow step of formation of the active, folded state. In the pituitary gland this would be a necessary pathway towards the active form. The storage of the hormone in the gland would offer enough time for this activation step to proceed.     

F plasmid partition depends on interaction of SopA with non-specific DNA

Bacterial ATPases belonging to the ParA family assure partition of their replicons by forming dynamic assemblies which move replicon copies into the new cell-halves. The mechanism underlying partition is not understood for the Walker-box ATPase class, which includes most plasmid and all chromosomal ParAs. The ATPases studied both polymerize and interact with non-specific DNA in an ATP-dependent manner. Previous work showed that in vitro, polymerization of one such ATPase, SopA of plasmid F, is inhibited by DNA, suggesting that interaction of SopA with the host nucleoid could regulate partition. In an attempt to identify amino acids in SopA that are needed for interaction with non-specific DNA, we have found that mutation of codon 340 (lysine to alanine) reduces ATP-dependent DNA binding > 100-fold and correspondingly diminishes SopA activities that depend on it: inhibition of polymer formation and persistence, stimulation of basal-level ATP hydrolysis and localization over the nucleoid. The K340A mutant retained all other SopA properties tested except plasmid stabilization; substitution of the mutant SopA for wild-type nearly abolished mini-F partition. The behaviour of this mutant indicates a causal link between interaction with the cell's non-specific DNA and promotion of the dynamic behaviour that ensures F plasmid partition.     

AP site structural determinants for Fpg specific recognition.

The binding of Escherichia coli and Lactococcus lactis Fapy-DNA glyosylase (Fpg) proteins to DNA containing either cyclic or non-cyclic abasic (AP) site analogs was investigated by electrophoretic mobility shift assay (EMSA) and by footprinting experiments. We showed that the reduced AP site is the best substrate analog for the E.coli and L.lactis enzymes ( K Dapp = 0.26 and 0.5 nM, respectively) as compared with the other analogs tested in this study ( K Dapp >2.8 nM). The 1,3-propanediol (Pr) residue-containing DNA seems to be the minimal AP site structure allowing a Fpg specific DNA binding, since the ethyleneglycol residue is not specifically bound by these enzymes. The newly described cyclopentanol residue is better recognized than tetrahydrofuran (for the E.coli Fpg, K Dapp = 2.9 and 25 nM, respectively). These results suggest that the hemiacetal form of the AP site is negatively discriminated by the Fpg protein suggesting a hydrogen bond between the C4'-hydroxyl group of the sugar and a Fpg residue. High-resolution hydroxyl radical footprinting using a duplex containing Pr shows that Fpg binds to six nucleotides on the strand containing the AP site and only the base opposite the lesion on the undamaged complementary strand. This comparative study provides new information about the molecular mechanism involved in the Fpg AP lyase activity.     

Recognition of cyclonucleoside lesions by the Lactococcus lactis FPG protein

Several purine and pyrimidine cyclonucleosides were found to be not recognized by several Escherichia coli and yeast DNA N-glycosylases. Interestingly, a non covalent complex was observed between the Lactoccocus lactis formamidopyrimidine-DNA glycosylases (Fpg-Ll) and the cyclonucleosides. This may provide new information on the mechanism involved in the activity of the latter enzyme.     

Complex oligomeric structure of a truncated form of DdrA: a protein required for the extreme radiotolerance of Deinococcus

In order to preserve their genome integrity, organisms have developed elaborate tactics for genome protection and repair. The Deinococcus radiodurans bacteria famous for their extraordinary tolerance toward high doses of radiations or long period of desiccation, possess some specific genes with unknown function which are related to their survival in such extreme conditions. Among them, ddrA is an orphan gene specific of Deinococcus genomes. DdrA, the product of this gene was suggested to be a component of the DNA end protection system. Here we provide a three-dimensional reconstruction of the Deinococcus deserti DdrA((1-160)) by electron microscopy. Although not functional in vivo, this truncated protein keeps its DNA binding ability at the wild-type level. DdrA((1-160)) has a complex three-dimensional structure based on a heptameric ring that can self-associate to form a larger molecular weight assembly. We suggest that the complex architecture of DdrA plays a role in the substrate specificity and favors an efficient DNA repair.     

The apparent buffer value of human blood for CO2 as a function of temperature

The influence of temperature on the acid-base status of normal human deoxygenated whole blood was studied in open systems (variable total CO2 content). (1) When the temperature was raised from 26 degrees C to 42 degrees C, the apparent buffering value of deoxygenated whole blood for CO2 increased by 7% of its value at 26 degrees C; this increase was not statistically significant. (2) Comparing the present data with those obtained previously from oxygenated whole blood in the same temperature range (Castaing & Pocidalo, 1979) indicates that arterial and venous blood have slightly different buffering capacities for CO2 in the 26 to 42 degrees C temperature range. It also suggests that, at physiological SO2 levels (SO2 greater than or equal to 30%), the apparent buffering value of venous blood for CO2 would be increased by at least 10% of its value at 26 degrees C when the temperature is raised to 42 degrees C. (3) It is concluded that pH stability would be reduced upon CO2 uptake within tissues with a high metabolism and therefore a high temperature.