Decreased virulence in stable,acapsular mutants ofCryptococcus neoformans

Six acapsular strains ofCryptococcus neoformans obtained by chemical mutagenesis failed to produce a capsulein vivo and were avirulent in mice following high dose intramuscular, intraperitoneal or intravenous inoculation. Peritoneal granulomas were observed in all animals inoculated with the acapsular mutants. These granulomas were characterized by a large central mass consisting of intact, degenerating and necrotic yeast cells. This was surrounded by concentric layers of a broad band of histiocytes, a narrow band of fibroblasts, and around the periphery, a mass of lymphocytes and plasma cells. These isolates did not revert to an encapsulated or virulent state after more than a year of subculturing or 18 passages through mice.     

Regulation of adenylate cyclase in E. coli

The intracellular concentrations of cAMP in Escherichia coli are regulated mainly by control of the activity of adenylate cyclase. Withdrawal of the carbon source from the growth medium causes a gradual reduction of cellular energy and a dramatic stimulation of cyclase activity. Manipulations of the proton gradient at the cell membrane of ATP synthase-deficient E. coli (unc-) revealed that this part of the energy compartment is not responsible for the starvation-induced stimulation of cyclase. Neither is the ATP pool involved in regulation of the activity of the cyclase. The intracellular concentrations of ATP were experimentally lowered by purine starvation of auxotrophs, by inhibition of purine synthesis using amethopterin, or by affecting ATP synthesis using arsenate. None of these conditions led to stimulation of cyclase activity. The control of cyclase is exerted not via the energy pools but via uptake systems of energy substrates independent of whether the substrate can be metabolized or not, or how the transport is energized. The stringent coupling between these transport systems and cyclase activity enables the cell to react instantaneously to changes in its environment.     

Indomethacin inhibition of ovulation in the cow

Indomethacin or saline was administered via intramuscular, intrauterine or intraovarian routes to dairy cows, within 24 h after standing oestrus was first observed. The incidence of ovulation was determined at slaughter. All of the saline-treated cows (18/18) ovulated. Ovulation was not blocked after intramuscular injection (0/6) or intrauterine infusion (0/6) of indomethacin. In all cows, ovulation was blocked after intraovarian injection (6/6) of indomethacin. These findings add support to the hypothesis that prostaglandins play an essential role in ovulation in the cow as in many other mammalian species.     

Limited proteolysis of human erythrocyte Ca2+-ATPase in membrane-bound form. Identification of calmodulin-binding fragments

Water-soluble and membrane-bound calmodulin-binding polypeptides formed upon limited proteolysis of erythrocyte ghosts were isolated by means of affinity chromatography. Immune blotting revealed that all isolated fragments originated from Ca2+-ATPase. Among the fragments obtained those having formed an acylphosphate intermediate were identified. The N-terminal residue of purified intact Ca2+-ATPase was shown to be blocked (probably acylated).     

Characteristics of different cytoplasmic and nuclear estrogen receptors appearing with continuous hormonal exposure

Biochemical properties of cytosol estrogen receptor (ERC) and nuclear estrogen receptor (ERN) from rat uteri continuously exposed in vivo to 17 beta-[2,4,6,7-3H] estradiol ( [3H]E2) for 6 h have been studied on the basis of immunological recognition and chromatographic elution patterns. Overall concentrations of ERC and ERN did not change during this time period when receptor-saturating concentrations of [3H]E2 were maintained (Jakesz, R., Kasid, A., and Lippman, M. E. (1983) J. Biol. Chem. 258, 11798-11806); however, biochemical characteristics were different in ERC and ERN after short or long term hormonal exposure. When ERC from rats treated with estradiol for 30 min was applied to HAP or DEAE columns, two different ER binding components were seen. DNA binding in a cell-free system revealed that these binding components represented an activated and a nonactivated ERC population. After long term hormonal exposure (6 h), only one component of ERC with low DNA binding could be shown despite the preservation of an equivalent quantity of cytoplasmic binding activity. This binder does not react with a monoclonal antibody directed against extranuclear estrogen receptor species. These data suggest disappearance of the activated ERC population, with appearance of a new, immunologically nonrecognizable ERC species with 6 h of continuous hormonal exposure. Elution profiles of ERN on HAP chromatography reveal 2 different binding components at 30 min and at 6 h of continuous [3H]E2 exposure. There is an increase of the population eluted at higher molarity after 6 h of in vivo treatment. This later eluting binding component is the major DNA binder in vitro. ERN from both time points are recognized immunologically by monoclonal antibody. After reaction with the antibody, the sedimentation coefficient shifted to 8-9 S on sucrose gradients, but the previously described faster sedimentation of ERN extracted 6 h after injection persisted. We conclude that ER in both cellular compartments undergoes time-dependent alterations, which may be involved in the initiation of hormone action.     

Furosemide-sensitive Na+-K+ cotransport and cellular metabolism in human erythrocytes

Metabolic depletion of human red cells with 2-deoxy-D-glucose in the presence of EGTA decreased ATP to about 4% of the initial value and increased total ouabain- and furosemide-resistant Na+ and K+ effluxes by 20% and 100%, respectively, and furosemide-sensitive Na+ and K+ effluxes by 100% and 60%, respectively. When ATP was restored, all the components of Na+ and K+ fluxes measured returned to baseline levels suggesting a metabolic dependence.     

The Role of Surface Water and Light on Differentiation in the Cellular Slime Molds

A key environmental factor in inducing final fruiting body differentiation in the migrating slugs of cellular slime molds is loss of contact with a surface film of water. If the slug tip reaches above the water film, fruiting tends to occur, but if it stays in contact with the surface water, continued migration is favored. Light is effective in promoting fruiting only if the phototactic slugs orient away from surface (as with overhead light) and therefore, only indirectly affects differentiation.