A serological comparison of the three morphological phases of Coccidioides immitis; complement fixation tests with anti-Histoplasma capsulatum serum

Summary The results of this study indicated that antigens prepared from the three morphological phases ofCoccidioides immitis differed in their complement fixing activity with anti-Histoplasma capsulatum pooled serum. Spherule antigens were serologically less active in tests with the anti-H. capsulatum pooled serum than antigens prepared from arthrospores and from mycelium.Antigenic determinants which are common toC. immitis andH. capsulatum appeared to be located on the intact arthrospore cellular surface but not on the surface of spherule cells.Part of a dissertation submitted to the Graduate School of Duke University in partial fulfillment of requirements for the Ph. D. degree.This work was supported by contract with the Department of the Army, Fort Detrick, Frederick, Maryland.In conducting the research reported herein, the investigators adhered to Guide for Laboratory Animal Facilities and Care established by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, NAS-NRC.     

Ras interaction with the GTPase-activating protein (GAP)

Biologically active forms of Ras complexed to GTP can bind to the GTPase-activating protein (GAP), which has been implicated as possible target of Ras in mammalian cells. In order to study the structural features of Ras required for this interaction, we have evaluated a series of mutant ras proteins for the ability to bind GAP and a series of Ras peptides for the ability to interfere with this interaction. Point mutations in the putative effector region of Ras (residues 32-40) that inhibit biological activity also impair Ras binding to GAP. An apparent exception is the Thr to Ser substitution at residue 35; [Ser-35]Ras binds to GAP as effectively as wild-type Ras even though this mutant is biologically weak in both mammalian and S. cerevisiae cells. In vitro, [Ser-35]Ras can also efficiently stimulate the S. cerevisiae target of Ras, adenylyl cyclase, indicating that other factors may influence Ras/protein interactions in vivo. Peptides having Ras residues 17-44 and 17-32 competed with the binding of Ras to E. coli-expressed GAP with IC50 values of 2.4 and 0.9 microM, respectively, whereas Ras peptide 17-26 was without effect up to 400 microM. A related peptide from the yeast GTP-binding protein YPT1 analogous to Ras peptide 17-32 competed with an IC50 value of 19 microM even though the YPT1 protein itself is unable to bind to GAP. These results suggest that determinants within Ras peptide 17-32 may be important for Ras binding to GAP.     

The role of mast cell degranulation products in mast cell hyperplasia. I. Mechanism of action of nerve growth factor

A variety of mast cell degranulating agents have previously been shown to induce mast cell hyperplasia in adult rats. In neonates 2.5 S nerve growth factor (NGF) induces a hyperplasia of both mucosal and connective tissue mast cells (MMC and CTMC). We have examined the role of the potent mast cell degranulating properties of NGF on its ability to induce mast cell hyperplasia. Administration of NGF in combination with the mast cell stabilizing agent disodium cromoglycate was found to abrogate the CTMC hyperplasia induced by NGF alone. Treatment of neonatal rats with the alternate degranulating agent compound 48/80 was found to induce a limited CTMC but not a MMC hyperplasia. A supernatant obtained by degranulating purified adult rat peritoneal mast cells with anti-IgE was found to induce hyperplasia of the CTMC population similar to that observed with NGF administration. However, this degranulation product supernatant only induced a limited MMC hyperplasia as judged by RMCP II content of the tissues. These results suggest that NGF has dual action inducing mast cell hyperplasia; CTMC hyperplasia being dependent on the ability of NGF to degranulate mast cells. MMC hyperplasia induced by NGF is independent of CTMC degranulation. Degranulation products from peritoneal mast cells act to increase both MMC and CTMC populations in the neonate. These data suggest that the CTMC population may be regulated by an autocrine positive feedback mechanism in vivo.     

Evidence of a Monoaminergic-Cholinergic Imbalance Related to Visual Hallucinations in Lewy Body Dementia

Senile dementia of Lewy body type is characterized clinically by a relatively acute onset of fluctuating memory loss and confusion, frequently accompanied by visual hallucinations. Neurochemical analyses of temporal cortex has revealed a distinction between hallucinating and nonhallucinating patients in both cholinergic and monaminergic transmitter activities. In contrast with the cholinergic enzyme choline acetyltransferase, which was more extensively reduced in hallucinating individuals, serotonergic S2 receptor binding and both dopamine and serotonin metabolites were significantly decreased in nonhallucinating cases. These results suggest that an imbalance between monaminergic and cholinergic transmitters is involved in hallucinogenesis in the human brain.     

Kinetics of insulin action on protein synthesis in isolated adipocytes. Ability of glucose to selectively desensitize the glucose transport system without altering insulin stimulation of protein synthesis

When adipocytes were exposed to [3H]leucine for times ranging from 5 to 180 s, leucine was found to enter cells rapidly and equilibrate with the cell interior within 5 s. After an additional 15-30 s [3H]leucine was incorporated into nascent protein, and the rate of incorporation was linear for up to 6 h in both control and insulin-treated cells. Since treatment of adipocytes with 10 ng/ml insulin enhanced the rate of leucine incorporation 2-3-fold with minimal or no effect on the rate of protein degradation or leucine uptake, we conclude that the predominant effect of insulin is on enhancement of protein synthesis. To assess the time required for insulin to stimulate protein synthesis, we preincubated cells with 10 ng/ml of insulin for various times from 2 to 30 min and then measured [3H]leucine incorporation into protein during a 4-min assay. These results revealed that the insulin stimulation of protein synthesis is rapid (t 1/2 of 4.4 min), but 9-fold slower than insulin activation of glucose transport (t 1/2 less than 0.5 min under identical conditions). In contrast to the rapidity of insulin activation, we found that deactivation proceeded at much slower rates (t 1/2 of 32 and 21 min for protein synthesis and glucose transport, respectively). Desensitization of the glucose transport system has previously been shown to occur after adipocytes are exposed to high glucose and insulin. To examine the specificity of desensitization, we treated cells for 6 h with 20 mM glucose and 25 ng/ml insulin and then examined insulin sensitivity and maximal insulin responsiveness of both the glucose transport and protein synthesis systems. After treatment, the glucose transport was markedly insulin-resistant (60% loss in maximal insulin responsiveness and a marked loss in insulin sensitivity), whereas the protein synthesis system exhibited neither diminished insulin responsiveness nor loss of insulin sensitivity. In fact, insulin sensitivity actually increased, as indicated by the finding that less insulin was required to stimulate protein synthesis (insulin ED50 values of 0.25 and 18 ng/ml at 0 and 6 h of treatment). From these studies we conclude that desensitization of the glucose transport system by glucose and insulin treatment appears to be specific for this particular effector system and does not reflect a state of generalized cellular insulin resistance.     

Molecular characterization by high resolution isoelectric focusing of the products encoded by the class II region loci of the MHC in humans. II. DP alpha and DP beta gene variants

To characterize the molecular polymorphism of the DP alpha and DP beta gene products, the HLA-DP molecules expressed by more than 200 cell lines were individually immunoprecipitated by using the mAb B7/21 and their neuraminidase-treated DP alpha and DP beta chains analyzed in IEF gels. These cell lines, most of them from members of 32 families, allowed the definition, by segregation analysis, of the IEF patterns of the DP polypeptide chains encoded by 129 distinct haplotypes. Both DP alpha and DP beta chains display polymorphic IEF-banding patterns. Two DP alpha (A and B) and seven DP beta (A, B, C, D, E, F, and G) IEF variants were characterized. The DP alpha B variant was found in linkage disequilibrium with both DP beta B and DP beta D. Linkage disequilibrium was also encountered with alleles at the DR and DQ loci. Finally, the correlations between the IEF DP alpha and DP beta variants and the primed lymphocyte test-defined HLA-DP specificities were determined by using a panel of 24 primed lymphocyte test-typed cell lines.     

Inhibin secretion during the rat estrous cycle: relationships to FSH secretion and FSH beta subunit mRNA concentrations

Serum inhibin and FSH and FSH beta subunit mRNA levels were measured at 3h intervals throughout the 4 day estrous cycle in female rats and hourly between 1000 and 2400 h of proestrus. On proestrus, serum inhibin concentrations fell during the late morning-early afternoon, then increased transiently during the late afternoon gonadotropin surges. Inhibin levels decreased during the late evening of proestrus, coincident with the FSH surge-related rise in FSH beta mRNA levels. Serum inhibin remained relatively stable during estrus and early metestrus, but rose during the late evening of metestrus and remained elevated until early diestrus. FSH beta mRNA levels were elevated on late estrus and early metestrus and declined during the evening of metestrus as serum inhibin levels increased. These data show that concentrations of serum inhibin change during the estrous cycle and that a general inverse relationship exists between serum inhibin and FSH levels and FSH beta mRNA concentrations in the pituitary. This suggests that inhibin may inhibit FSH beta gene expression and FSH secretion during the 4 day cycle in female rats.     

Substrate kinetics of the tonoplast h-translocating inorganic pyrophosphatase and its activation by free mg

To clarify the kinetic characteristics and ionic requirements of the tonoplast H⁺-translocating inorganic pyrophosphatase (H⁺-PPiase), PPi hydrolysis and PPi-dependent H⁺ transport were studied in tonoplast vesicles isolated from leaf mesophyll tissue of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie. The tonoplast H⁺-PPiase showed an absolute requirement for a monovalent cation and exhibited hyperbolic kinetics with respect to cation concentration. H⁺-PPiase activity was maximal in the presence of K⁺ (K₅₀ approximately 3 millimolar), with PPi-dependent H⁺ transport being more selective for K⁺ than PPi hydrolysis. When assayed in the presence of 50 millimolar KCl at fixed PPi concentrations, H⁺-PPiase activity showed sigmoidal kinetics with respect to total Mg concentration, reflecting a requirement for a Mg/PPi complex as substrate and free Mg²⁺ for activation. At saturating concentrations of free Mg²⁺, H⁺-PPiase activity exhibited Michaelis-Menten kinetics towards MgPPi²⁻ but not Mg₂PPi, demonstrating that MgPPi²⁻ was the true substrate of the enzyme. The apparent K_m (MgPPi²⁻) for PPi hydrolysis (17 micromolar) was significantly higher than that for PPi-dependent H⁺ transport (7 micromolar). Free Mg²⁺ was shown to be an allosteric activator of the H⁺-PPiase, with Hill coefficients of 2.5 for PPi hydrolysis and 2.7 for PPi-dependent H⁺ transport. Half-maximal H⁺-PPiase activity occurred at a free Mg²⁺ concentration of 1.1 millimolar, which lies within the range of accepted values for cytosolic Mg²⁺. In contrast, cytosolic concentrations of K⁺ and MgPPi²⁻ appear to be saturating for H⁺-PPiase activity. We propose that one function of the H⁺-PPiase may be to act as an ancillary enzyme that maintains the proton-motive force across the vacuolar membrane when the activity of the tonoplast H⁺-ATPase is restricted by substrate availability. As ATP levels decline in the cytosol, free Mg²⁺ would be released from the MgATP²⁻ complex, thereby activating the tonoplast H⁺-PPiase.