CCR5- and CXCR4-Utilizing Strains of Human Immunodeficiency Virus Type 1 Exhibit Differential Tropism and Pathogenesis In Vivo

CCR5-utilizing (R5) and CXCR4-utilizing (X4) strains of human immunodeficiency virus type 1 (HIV-1) have been studied intensively in vitro, but the pathologic correlates of such differential tropism in vivo remain incompletely defined. In this study, X4 and R5 strains of HIV-1 were compared for tropism and pathogenesis in SCID-hu Thy/Liv mice, an in vivo model of human thymopoiesis. The X4 strain NL4-3 replicates quickly and extensively in thymocytes in the cortex and medulla, causing significant depletion. In contrast, the R5 strain Ba-L initially infects stromal cells including macrophages in the thymic medulla, without any obvious pathologic consequence. After a period of 3 to 4 weeks, Ba-L infection slowly spreads through the thymocyte populations, occasionally culminating in thymocyte depletion after week 6 of infection. During the entire time of infection, Ba-L did not mutate into variants capable of utilizing CXCR4. Therefore, X4 strains are highly cytopathic after infection of the human thymus. In contrast, infection with R5 strains of HIV-1 can result in a two-phase process in vivo, involving apparently nonpathogenic replication in medullary stromal cells followed by cytopathic replication in thymocytes.     

Racism and sexism in medically assisted conception

Despite legislation and public education, racism and sexism are alive and well. Though pre-conceptive gender selection may enhance procreative liberty, this technology presents two disturbing questions. First, does sex selection represent underlying parental sexism? Second, by performing gender selection, do medical professionals perpetuate sexism? It will be maintained that pre-conceptive sex selection is sexist as it reflects parental anticipation of stereotypical gender based behavior. Perhaps even more incriminating, sex selection forces parents to prefer one sex over another, to place a value on gender. This emphasis on sex conflicts with societal goals which urge, and often legally require, individuals to ignore gender. We will assert that pre-conceptive gender selection exemplifies sexism in its purest most blatant form as prior to conception, before parents can possibly know anything about their child, gender dominates the calculus of a child’s worth. We will also emphasize that physicians, by facilitating sex selection, legitimize the motivations of their patients and provide de facto support of sexism. In a similar vein, arguments against pre-conceptive race selection will be made.     

Chloroplast Inner-Envelope ATPase Acts as a Primary H+ Pump

The stromal pH of the chloroplast must be maintained higher than that of the surrounding cytosol for photosynthetic carbon assimilation to occur. Experimental evidence demonstrating how this is accomplished in the plant cell is lacking. In the experiments reported here, we studied H+ and K+ flux across membranes of purified chloroplast inner-envelope vesicles. We were able to demonstrate ATP-dependent transport of both cations across the membranes of these vesicles. The data presented document the presence of an H+-pump ATPase in the chloroplast envelope. Energy-dependent K+ flux across these membranes occurs as a consequence of primary H+ pumping. The H+-pumping activity demonstrated in this report is consistent with a model involving the activity of this envelope ATPase as a primary mechanism facilitating a stroma:cytosol [delta]pH.     

Oxidation of prostacyclin and its analogs by three 15-hydroxyprostaglandin dehydrogenases

A study of the oxidation of prostacyclin and some of its analogs by three 15-hydroxyprostaglandin dehydrogenases was undertaken to determine the structural features of these compounds which might influence their rate of enzymatic inactivation. The effect of some structural changes seemed to be determined by the substrate specificity of individual enzymes. Other changes influenced the rate of oxidation by all three enzymes similarily. Among this latter group it was noted that a 15S hydroxyl group is necessary for oxidation to occur and that steric changes in the carboxy side chain and structural changes in the epoxy ring have a greater effect on the affinity of the substrate for the enzyme than on its maximum rate of oxidation. Certain analogs of prostacyclin are not substrates for one or more of the enzymes tested. Of these, (5S)-9-deoxy-5,9α-epoxy-PGF₁ and its methyl ester are potent inhibitors of only the placental enzyme—an interesting case of apparent selective metabolic regulation.     

Analysis of the Distribution of Potassium-stimulated Adenosine Triphosphatase Activity in Soybean Root

The distribution of activity of a potassium-stimulated ATPase associated with the plasma membrane was determined in 4-day-old soybean roots. Changes in protein-based specific activity of the enzyme coincided with developmental changes in the root. Activity was low in the region of the root cap, increased to a maximum in the meristematic region, decreased to a minimum as cell elongation proceeded, and then increased as lateral root development began. Analysis of the data indicated that fluctuations in enzyme activity can be described by a three-phase system which can be approximated by a linear-linear-linear piece-wise regression curve. The need for constructing a biological model to describe plasma membrane development is suggested.     

Influence of age on brain vascular and cardiovascular monoamine oxidase activity in the rat

Monoamine oxidase (MAO) activity in brain microvessels and cardiovascular tissues was examined in rats of different age. MAO activity continued to increase with age in the heart, but in contrast, reached maximum activity in three weeks in the aorta, mesenteric artery and mesenteric vein. Between 7 and 60 weeks, there was a small decline in the MAO activity in the testicular artery. The highest MAO activity was found in the cerebral microvessels and increased with age. The half-life of MAO was estimated in the heart and peripheral blood vessels in young and old animals. The half-life of cardiac MAO was increased with age whereas that of the mesenteric vein, mesenteric artery and aorta remained constant between 7 and 112 weeks. Thus an explanation for this increased cardiac MAO activity in old rats was a reduced rate of degredation of this enzyme. The high activity of the enzyme in the brain microvessels suggests that it may participate in regulating the influx and efflux of monoamines in the central nervous system.     

Binding of glycerol by microtubule protein.

When microtubules are purified by polymerization and depolymerization in a buffer containing glycerol, some glycerol becomes bound to the microtubule protein and is not removable by gel filtration or by prolonged dialysis. Both 6s tubulin and larger aggregates containing tubulin and accessory proteins bind glycerol. The 6s fraction has associated with it about 5 moles of glycerol per mole of tubulin dimer; 3 moles are exchangeable upon polymerization-depolymerization and 2 moles are not. The aggregate fraction has associated with it about 22 moles of glycerol per mole of tubulin dimer; approximately 11 moles are exchangeable and 11 moles are not.     

Different arrangements of protein subunits and single-stranded circular DNA in the filamentous bacterial viruses fd and Pf1

A single-stranded circular DNA molecule of 6690 ± 450 nucleotides accounts for 5.5 ± 0.3% of the mass of Pf1 virus. The remaining mass is contributed almost entirely by subunits of the major coat protein. A non-integral nucleotide to subunit ratio of 0.87 ± 0.05 is calculated from the DNA content, the average nucleotide mass (309), and the known mass of one protein subunit (4609). There are therefore 7690 ± 680 major coat protein subunits in the virus. The virus length determined by electron microscopy is 1960 ± 70 nm. The data give an average axial distance of 2.55 ± 0.24 Å between protein subunits in dry virus. Since there is an up strand and a down strand of the circular DNA within the virus filament, an axial distance between bases in a given strand of 5.9 ± 0.5 Å is calculated. Available X-ray data show that an axial repeat of 72 Å, or slightly less, would be expected for dry Pf1 virus (0% relative humidity). A structural model in which 27 protein subunits and 24 nucleotides are contained in this repeat would be consistent with our data. The DNA conformation and the subunit packing in Pf1 differ considerably from those in fd, even though both are filamentous viruses containing single-stranded circular DNA. The uncertainties cited are 95% confidence limits.     

Stromal pH and Photosynthesis Are Affected by Electroneutral K and H Exchange through Chloroplast Envelope Ion Channels

Potassium movement across the limiting membrane of the chloroplast inner envelope is known to be linked to counterex-change of protons. For this reason, K⁺ efflux is known to facilitate stromal acidification and the resultant photosynthetic inhibition. However, the specific nature of the chloroplast envelope proteins that facilitate K⁺ fluxes, and the biophysical mechanism which links these cation currents to H⁺ counterflux, is not characterized. It was the objective of this work to elucidate the nature of the system regulating K⁺ flux linked to H⁺ counterflux across the chloroplast envelope. In the absence of external K⁺, exposure of spinach (Spinacia oleracea) chloroplasts to the K⁺ ionophore valinomycin was found to increase the rate of K⁺ efflux and H⁺ influx. These data were interpreted as suggesting that H⁺ counterexchange must be indirectly linked to movement of K⁺ across the envelope. Studies using the K⁺ channel blocker tetraethylammonium indicated that K⁺ likely moves, in a uniport fashion, into or out of the stroma through a monovalent cation channel in the envelope. Blockage of K⁺ efflux from the stroma by exposure to tetraethylammonium was found to restrict H⁺ influx, further substantiating an indirect linkage of these cation currents. Further studies comparing the effect of exogenous H⁺ ionophores and K⁺/H⁺ exchangers suggested that K⁺ uniport through this ion channel likely is the main endogenous pathway for K⁺ currents across the envelope. These experiments were also consistent with the presence of a proton channel in the envelope. Movement of H⁺ through this channel was speculated to be regulated and rate limited by an electroneutral requirement for K⁺ countercurrents through the separate K⁺ uniport pathway. K⁺ and H⁺ fluxes across the chloroplast envelope were envisioned to be interrelated via this mechanism. The significant effect of cation currents across the envelope, as mediated by these channels, on photosynthetic capacity of the isolated chloroplast was also demonstrated.