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Biomedical subjects

C Klein

Publications and source records attributed to C Klein.

At least 379 records · Page 21Linked to original sources
PubMed1982

Differential interference by azathioprine and 6-mercaptopurine with antibody-mediated immunoregulation: synergism of azathioprine and antibody in the control of an immune response.

Comparative studies on the effects of immunosuppressive agents azathioprine (AZ) and 6-mercaptopurine (6-MP) in antibody-mediated immunoregulation are reported. To determine the degree of interference of these agents with the generation of antibody molecules controlling an anti-SRBC response, the donors of mouse anti-SRBC sera were given daily doses of the drugs. Primary antisera from AZ-treated donors were not significantly inhibited by daily doses of 180, 270, and 360 mumol/kg in their ability to suppress the direct PFC response; on the other hand 6-MP was inhibitory at the two higher equimolar dose levels. When the antisera were used in the antibody-dependent cellular cytotoxicity (ADCC) and phagocytosis (AD phi) assays, similar differential effects of the two agents were found. Multiple doses of AZ and 6-MP given to the donors of ADCC effector cells enhanced the capacity of these cells to lyse antibody-sensitized SRBC target cells. The enhancement of ADCC with 6-MP was less manifest than that with AZ. When injected before the antigen, AZ acted synergistically with the antibody in the control of the direct PFC response. Possible mechanisms by which AZ can interact with antibody-mediated immune regulation are discussed.

Animals↗
PubMed1981

A protein kinase of the plasma membrane of Dictyostelium discoideum.

D. discoideum amoebae were found to phosphorylate plasma membrane proteins when intact cells were incubated with either [gamma-32P]ATP or [32P]phosphate. In the first case, the incorporation was largely a consequence of the hydrolysis of [gamma-32P]ATP, cellular uptake of the generated [32P]phosphate and its subsequent incorporation into ATP. When the contribution of this process to the phosphorylating activity of intact cells was eliminated, an ecto-protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) activity could be demonstrated. As amoebae progressed through their aggregation program, they showed a decreased ability to phosphorylate their plasma membrane when incubated with [gamma-32 P]ATP or [32P]phosphate. Analysis of ATPase activity, permeability properties and the pattern of proteins phosphorylated by intact cells and isolated plasma membranes lead to the following conclusions: the lower levels of phosphorylation observed with starved cells reflected an altered uptake of [32P]phosphate by these cells rather than a significant change in the plasma membrane protein kinase activity. Neither the substrates nor the activity of the ecto-protein kinase was dramatically altered during starvation.

Cell Membrane↗
PubMed1981

Stability of lactate dehydrogenase. II. Hybrids and geometric isomers.

Hybrids of lactate dehydrogenases from pig heart and muscle and from chicken heart and pig heart were obtained by the freeze-thaw method [1,2]. Ion-exchange chromatography of the resulting mixtures of hybrids yielded unusual elution patterns, i.e., the 2 + 2 hybrids (HP2MP2 and HC2HP2) were eluted in two separate peaks. These subforms were concluded to result from partial resolution of the three geometric isomers. The hybrids of chicken heart and pig heart lactate dehydrogenase showed three distinct levels of stability. The characteristics temperatures of denaturation were 61.5 degrees C for HP4, HCHP3 and HC2HP2I; 71 degrees C for HC2HP2II and HC3HP and 76.5 degrees for HC4. The resistance towards thermal denaturation thus seemed to be governed by the least stable dimer within the tetrameric enzyme. The arrangement of stabilities of the dimers was in excellent agreement with the number of additional ion pairs between Arg241 (chicken) and Asp57 (chicken and pig) [3] within the Q-contact areas. The rate-determining step of thermal denaturation of lactate dehydrogenase was concluded to comprise the distortion or dissociation of one or two Q-contacts of the tetramer.

Animals↗
PubMed1981

Binding of adenosine 3':5'-monophosphate to plasma membranes of Dictyostelium discoideum amoebae.

A plasma membrane preparation from Dictyostelium discoideum amoebae which contains the high affinity cAMP receptor is described. Ligand specificity and the kinetics of cAMP association and dissociation using isolated plasma membranes were similar to those of intact cells. The changes in cAMP binding activity which occur as cells proceed through their aggregation program were also reflected in the membrane preparations. However, neither the low affinity cAMP binding site nor the oscillatory cAMP binding behavior observed on intact cells was detected with the membrane preparations.

Cell Membrane↗
PubMed1981

Photoaffinity labeling of the cell surface adenosine 3':5'-monophosphate receptor of Dictyostelium discoideum and its modification in down-regulated cells.

The cAMP cell surface receptor of Dictyostelium discoideum amoebae was identified by the use of the photoaffinity analogue 8-N3-[32P]cAMP. Labeling by intact cells of one component, identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography, could be specifically inhibited by the presence of nonradioactive cAMP. The component, P45 (apparent molecular weight of 45,000), was not identified on vegetative cells but was labeled with increasing intensity as cells differentiated and increased their levels of surface cAMP binding sites. Developmental mutants, starved under conditions where they do not express significant levels of cAMP binding sites, did not incorporate radioactivity into this protein. These mutants did label P45 when starved under differentiation-inducing conditions such that their levels of surface cAMP binding sites increased. P45 co-purified with the plasma membrane fraction isolated from cells to which 8-N3-[32p]cAMP had been covalently bound. Down-regulated amoebae, which displayed approximately 25% of the binding activity of untreated cells, did not label P45. These cells did, however, label a new component with an apparent molecular weight of 47,000 (P47).l The appearance of this component represented the only discernible difference in labeling profile under these conditions. As in the case of P45, radioactive incorporation into P47 did not occur if the photoactivation of 8-N3-[32P]cAMP was performed in the presence of nonradioactive cAMP.

Affinity Labels↗
PubMed1981

Impaired maturation of Purkinje cells in the fetal alcohol syndrome of the rat. Light and electron microscopic investigations.

Alcohol was administered in a vitamin-supplemented liquid diet (Stardit) to Wistar rats 4 weeks before mating and during pregnancy. Of the daily calories 38--40% were supplied by alcohol and by isocaloric sucrose in the controls. Offspring of alcohol drinking dams showed a reduced birth weight and gained weight less rapidly than the controls. On day 3, 4, 7, 12, 17 and 21, experimental animals and controls were perfused for histological and electron microscopic investigations. Morphometric analysis of the cerebella (Fol. 5 and Fol. 8) showed no difference in the number of Purkinje cells. However, on day 7 the Purkinje cell nuclei of experimental pups were significantly smaller. This difference disappeared at day 12. Electron microscopic investigations in the 4, 7, and 12 days old experimental animals revealed a delayed cytoplasmic maturation of Purkinje cells which mainly involved the rough endoplasmic reticulum. At 17 days, there was no difference between the two groups. These data are discussed in relation to alcohol-induced metabolic changes in the brain.

Animals↗
PubMed1980

Pancreatic polypeptide (PP)- and glucagon cells in the pancreatic islet of Xiphophorus helleri H. (Telecostei). Correlative immunohistochemistry and electron microscopy.

Correlative immunohistochemical and electron microscopical studies on the pancreatic islet of the telecost fish Xiphorphorus helleri using antibodies to pancreatic polypeptide (PP) and glucagon show that separate cell types are responsible for the production of these peptides. The PP-cells correspond to the previously described "A2-cells with round granules", while the "A2-cells with crystalline granules" are the true glucagon cells. An earlier suggestion that there are two types of glucagon cells in teleost islets is therefore withdrawn.

Animals↗
PubMed1980

Influence of hypo- and hyperthyroidism on noradrenaline metabolism in brown adipose tissue of the developing rat.

We studied the noradrenaline content, and monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) activities in brown adipose tissue (BAT) of normal, hypothyroid, and hyperthyroid developing rat. In the newborn, thyroid hormones are necessary for the increase in noradrenaline content which occurs between 0 and 5 days. Hypothyroidism increases both MAO and COMT activities. Hyperthyroidism decreases MAO activity but not noradrenaline content or COMT activity. In the full-term fetus, hypothyroidism decreases noradrenaline content as in the newborn, and also decreases MAO and COMT activities. It is suggested that thyroid hormones could modulate BAT nonshivering thermogenesis by regulating the level of noradrenaline, the direct mediator of heat production.

Adipose Tissue, Brown↗
PubMed1980

Tyrosine hydroxylase activity and catecholamine content in the adrenals of young hypo- and hyperthyroid rats.

The weight, the tyrosine hydroxylase (TH) activity and the catecholamine (noradrenaline and adrenaline) content of young rat adrenals have been measured from birth to 20 days after birth in relation to hypo- and hyperthyroidism. Hypothyroidism impairs the adrenal growth, while hyperthyroidism has no effect on the adrenal weight. Hypothyroidism is associated with an enhancement of TH activity and catecholamine content. In hyperthyroid rats, the increase in TH activity and catecholamine content is slower than in controls. In adult animals, TH activity and catecholamine content are less affected by thyroid function.

Adrenal Glands↗
PubMed1979

A slowly dissociating form of the cell surface cyclic adenosine 3':5'-monophosphate receptor of Dictyostelium discoideum.

Experiments using a phosphodiesterase-minus mutant of Dictyostelium discoideum indicate that ligand-induced loss of cell surface cyclic adenosine 3':5'-monophosphate binding sites (down regulation) can be evoked with concentrations of cyclic adenosine 3':5'-monophosphate as low as 10(-8) M. The loss of receptor sites is observed after 5 min of cell preincubation with cyclic adenosine 3':5'-monophosphate and can be as extensive as 75 to 80%. This decrease in binding sites is correlated with the appearance of a slowly dissociating cyclic adenosine 3':5'-monophosphate binding component. Radioactive cyclic adenosine 3':5'-monophosphate bound to this form of receptor cannot be competed for by nonradioactive cyclic adenosine 3':5'-monophosphate or adenosine 5'-monophosphate and is not accessible to hydrolysis by cyclic adenosine 3':5'-monophosphate phosphodiesterase. The extent of appearance of this binding component is dependent upon the concentration of cyclic adenosine 3':5'-monophosphate used to elicit the down regulation response and the temperature of the incubation medium.

Cyclic AMP↗