Predominant time scales in fission processes in reactions of S, Ti and Ni with W: zeptosecond versus attosecond

The inhibition of fusion by quasifission is crucial in limiting the formation of superheavy elements in collisions of heavy nuclei. Time scales of ∼10(-18)  s inferred for fissionlike events from recent crystal blocking measurements were interpreted to show either that quasifission itself is slower than previously believed, or that the fraction of slow fusion-fission is higher than expected. New measurements of mass-angle distributions for (48)Ti and (64)Ni bombarding W targets show that in these reactions quasifission is the dominant process, typically occurring before the system formed after contact has made a single rotation, corresponding to time scales of ≤10(-20)  s.

Disentangling effects of nuclear structure in heavy element formation

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.

Changed environmental conditions weaken sexual selection in sticklebacks

Environmental heterogeneity can cause the intensity and direction of selection to vary in time and space. Yet, the effects of human-induced environmental changes on sexual selection and the expression of mating traits of native species are poorly known. Currently, the breeding habitats of the three-spined stickleback Gasterosteus aculeatus are changing in the Baltic Sea because of eutrophication and increased growth of algae. Here we show that enhanced growth of filamentous algae increases the costs of mating by inducing an increase in the time and energy spent on courtship and mate choice. This is not followed by a concomitant increase in mate attraction, but instead the strength of selection on male red nuptial coloration and courtship activity is relaxed. Thus, the high investment into the costly sexually selected traits is maladaptive under the new conditions, and the mating system mediates a negative effect of the environmental change on the population. We attribute these environmentally induced changes in the benefit of the mating traits and in the strength of sexual selection to reduced visibility in dense vegetation. Anthropogenic disturbances hence affect the selection pressures that mould the species, which could have long-term effects on the viability and evolution of the populations.

Independent ion migration in suspensions of strongly interacting charged colloidal spheres

We report on systematic measurements of the low-frequency conductivity sigma in aqueous suspensions of highly charged colloidal spheres. Sample preparation in a closed tubing system results in precisely controlled number densities of 10(16) m-3 < or = n < or = 10(19) m-3 (packing fractions of 10(-7) < or = phi < or = 10(-2)) and electrolyte concentrations of 10 < or = c < or = 10(-3) mol l-1. Due to long-range Coulomb repulsion, some of the systems show a pronounced fluid or crystalline order. Under deionized conditions we find sigma to depend linearly on the packing fraction with no detectable influence of the phase transitions. Further, at constant packing fraction sigma increases sublinearly with the increasing number of dissociable surface groups N. As a function of c the conductivity shows pronounced differences depending on the kind of electrolyte used. We propose a simple yet powerful model based on the independent migration of all species present and the additivity of the respective conductivity contributions. It takes account of small ion macro-ion interactions in terms of an effectively transported charge. The model successfully describes our qualitatively complex experimental observations. It further facilitates quantitative estimates of sigma over a wide range of particle and experimental parameters.

Synthesis of 3'-O2-(azaheterocycle)-thymidines

The synthesis of 3'-O2-(azaheterocycle)-thymidines is presented from 1-thia-3-aza- 1,3-butadiene precursors (N-thioacylamidines). A variety of heterocycles is accessible using the dienic, the electrophilic or the nucleophilic reactivity of these thia-azabutadiene systems. 3'-O2-(azaheterocycle)-thymidine analogues are regarded as potential substrates to interfere with the DNA-polymerization process.

Mice deficient in lysosomal acid phosphatase develop lysosomal storage in the kidney and central nervous system

Lysosomal acid phosphatase (LAP) is a tartrate-sensitive enzyme with ubiquitous expression. Neither the physiological substrates nor the functional significance is known. Mice with a deficiency of LAP generated by targeted disruption of the LAP gene are fertile and develop normally. Microscopic examination of various peripheral organs revealed progredient lysosomal storage in podocytes and tubular epithelial cells of the kidney, with regionally different ultrastructural appearance of the stored material. Within the central nervous system, lysosomal storage was detected to a regionally different extent in microglia, ependymal cells, and astroglia concomitant with the development of a progressive astrogliosis and microglial activation. Whereas behavioral and neuromotor analyses were unable to distinguish between control and deficient mice, approximately 7% of the deficient animals developed generalized seizures. From the age of 6 months onward, conspicuous alterations of bone structure became apparent, resulting in a kyphoscoliotic malformation of the lower thoracic vertebral column. We conclude from these findings that LAP has a unique function in only a subset of cells, where its deficiency causes the storage of a heterogeneously appearing material in lysosomes. The causal relationship of the enzyme defect to the clinical manifestations remains to be determined.

Preparation and anti-HIV activity of N-3-substituted thymidine nucleoside analogs

A series of 22 derivatives of AZT substituted at the N-3 position of the thymine base were prepared and evaluated for anti-HIV activity in cell culture (Lai strain of HIV-1 in CEM-c113 cells). The AZT analogs bearing a N-3 amino group (7), a hydroxyalkyl chain (12f), and a phosphonomethyl (12k) substituent displayed activities in the 0.045-0.082 microM range. The analogs 12d, 12e, 12q, 15, and 19 were active at <0.5 microM concentration. Compound 18 in which two molecules of AZT are connected at N-3 via a two-carbon link and "dimer" 11 also displayed significant activity. To obtain information concerning the mechanism of RT inhibition by these AZT analogs, compounds 7, 12d, 12e, and 12q were incubated with recombinant HIV-1 RT in the presence of poly(A)-oligo[dT(12-18)] and poly(C)-oligo[dG(12-18)] template-primers. In contrast to AZT-TP (control), none of these nucleosides displayed any significant inhibition of RT in the recombinant enzyme assay, indicating that phosphorylation is a necessary prerequisite for activity.

Phenotype of arylsulfatase A-deficient mice: relationship to human metachromatic leukodystrophy

Metachromatic leukodystrophy is a lysosomal sphingolipid storage disorder caused by the deficiency of arylsulfatase A. The disease is characterized by progressive demyelination, causing various neurologic symptoms. Since no naturally occurring animal model of the disease is available, we have generated arylsulfatase A-deficient mice. Deficient animals store the sphingolipid cerebroside-3-sulfate in various neuronal and nonneuronal tissues. The storage pattern is comparable to that of affected humans, but gross defects of white matter were not observed up to the age of 2 years. A reduction of axonal cross-sectional area and an astrogliosis were observed in 1-year-old mice; activation of microglia started at 1 year and was generalized at 2 years. Purkinje cell dendrites show an altered morphology. In the acoustic ganglion numbers of neurons and myelinated fibers are severely decreased, which is accompanied by a loss of brainstem auditory-evoked potentials. Neurologic examination reveals significant impairment of neuromotor coordination.

Targeted disruption of the arylsulfatase B gene results in mice resembling the phenotype of mucopolysaccharidosis VI

Mucopolysaccharidosis VI (MPS VI) is a lysosomal storage disease with autosomal recessive inheritance caused by a deficiency of the enzyme arylsulfatase B (ASB), which is involved in degradation of dermatan sulfate and chondroitin 4-sulfate. A MPS VI mouse model was generated by targeted disruption of the ASB gene. Homozygous mutant animals exhibit ASB enzyme deficiency and elevated urinary secretion of dermatan sulfate. They develop progressive symptoms resembling those of MPS VI in humans. Around 4 weeks of age facial dysmorphia becomes overt, long bones are shortened, and pelvic and costal abnormalities are observed. Major alterations in bone formation with perturbed cartilaginous tissues in newborns and widened, perturbed, and persisting growth plates in adult animals are seen. All major parenchymal organs show storage of glycosaminoglycans preferentially in interstitial cells and macrophages. Affected mice are fertile and mortality is not elevated up to 15 months of age. This mouse model will be a valuable tool for studying pathogenesis of MPS VI and may help to evaluate therapeutical approaches for lysosomal storage diseases.

Betulinic acid derivatives: a new class of human immunodeficiency virus type 1 specific inhibitors with a new mode of action

A series of omega-undecanoic amides of lup-20(29)-en-28-oic acid derivatives were synthesized and evaluated for activity in CEM 4 and MT-4 cell cultures against human immunodeficiency virus type 1 (HIV-1) strain IIIB/LAI. The potent HIV inhibitors which emerged, compounds 5a, 16a, and 17b, were all derivatives of betulinic acid (3beta-hydroxylup-20(29)-en-28-oic acid). No activity was found against HIV-2 strain ROD. Compound 5a showed no inhibition of HIV-1 reverse transcriptase activity with poly(C).oligo(dG) as template/primer, nor did it inhibit HIV-1 protease. Additional mechanistic studies revealed that this class of compounds interfere with HIV-1 entry in the cells at a postbinding step.

Betulinic acid derivatives: a new class of specific inhibitors of human immunodeficiency virus type 1 entry

A novel series of omega-aminoalkanoic acid derivatives of betulinic acid were synthesized and evaluated for their activity against human immunodeficiency virus (HIV). The anti-HIV-1 activity of several members of this new series was found to be in the nanomolar range in CEM 4 and MT-4 cell cultures. The optimization of the omega-aminoalkanoic acid side chain is described. The presence of an amide function within the side chain was found important for optimal activity. RPR 103611 (14g), a statine derivative, was found to be inactive against HIV-1 protease, reverse transcriptase, and integrase as well as on gp120/CD4 binding. "Time of addition" experiments suggested interaction with an early step of HIV-1 replication. As syncytium formation, but not virus-cell binding, seems to be affected, betulinic acid derivatives are assumed to interact with the postbinding virus-cell fusion process.

Mice deficient for the lysosomal proteinase cathepsin D exhibit progressive atrophy of the intestinal mucosa and profound destruction of lymphoid cells

Mice deficient for the major lysosomal aspartic proteinase cathepsin D, generated by gene targeting, develop normally during the first 2 weeks, stop thriving in the third week and die in a state of anorexia at day 26 +/- 1. An atrophy of the ileal mucosa first observed in the third week progresses towards widespread intestinal necroses accompanied by thromboemboli. Thymus and spleen undergo massive destruction with fulminant loss of T and B cells. Lysosomal bulk proteolysis is maintained. These results suggest, that vital functions of cathepsin D are exerted by limited proteolysis of proteins regulating cell growth and/or tissue homeostasis, while its contribution to bulk proteolysis in lysosomes appears to be non-critical.