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Biomedical subjects

K Bauer

Publications and source records attributed to K Bauer.

At least 181 records · Page 10Linked to original sources
PubMed1988

The pho-controlled outer membrane porin PhoE does not contain specific binding sites for phosphate or polyphosphates.

Purified PhoE-porins were reconstituted into black lipid bilayer membranes, and the selectivity and size of the reconstituted pores were determined. Addition of polyphosphates influenced the internal charge situation of the pore resulting in a shift from anion to cation selectivity. However, the pore size as judged from single channel conductances was not influenced by the addition of polyphosphates. A strong inhibition of the pore conductance only occurred when Mg2+ was also present in the aqueous phase. The inhibition of the pore function is presumably caused by the formation of a chelate between the divalent cation and the polyphosphate. Nevertheless, neither this inhibition nor the selectivity shift are specific to phosphate, because both effects can be mimicked by other polyvalent anions such as citrate. Inhibition of the PhoE pore function by polyphosphate in in vivo experiments confirmed the results of in vitro experiments that polyphosphate is only able to affect the permeability of the outer membrane toward beta-lactam antibiotics if Mg2+ is present. The outcome of the in vivo and the in vitro experiments are consistent with the assumption that the PhoE-porins do not contain a specific binding site for phosphate or polyphosphates but are anion selective because of an excess of positively charged amino acids inside or at the surface of the pore.

Bacterial Outer Membrane Proteins↗
PubMed1988

Pore formation by pho-controlled outer-membrane proteins of various Enterobacteriaceae in lipid bilayers.

The structural genes of the PhoE porins of Klebsiella pneumonia, Enterobacter cloacae and Escherichia coli C, cloned in multicopy plasmids, were transfered into a porin-deficient E. coli K-12 strain, which was constitutive for the pho regulon, and the PhoE porins were isolated and purified. PhoE of Salmonella typhimurium could not be cloned but was isolated from a pho-constitutive strain. Reconstitution experiments with artificial lipid bilayer membranes showed that the different PhoE proteins formed pores exhibiting a single-channel conductance of about 200 pS at 0.1 M KCl. All PhoE porins formed anion-selective channels in KCl at neutral pH. The degree of the selectivity was dependent on the PhoE species. The different PhoE porins formed general diffusion pores similar to the general porins but exhibited a considerable advantage for the permeation of phosphate through the outer membrane as compared to the constitutive OmpC and OmpF porins of E. coli K-12.

Bacterial Outer Membrane Proteins↗
PubMed1988

Quantitative determination of human protein C. Evaluation of a "fast" functional assay in comparison to a "traditional" functional and an immunological assay.

A fast functional assay for protein C was evaluated and compared with a traditional functional and an enzyme linked immunosorbent assay in parallel for the same plasma samples derived from 43 healthy subjects, 12 patients with severe hepatic dysfunction, and 23 patients under stable oral anticoagulation. By all three test systems significantly lower levels of protein C were obtained in both groups of patients compared with normal subjects (p less than 0.0001). No significant between - assay differences were found in normal subjects and in patients with hepatic dysfunction; by correlation analysis coefficients higher than 0.8 were calculated between the measurements of the three tests. In patients under stable oral anticoagulation, however, the immunologic test yielded higher values than the traditional (p less than 0.05) and, more pronounced, the fast functional assay (p less than 0.0001); no or only borderline significant correlations between the results were found. In these patients protein C levels measured with the traditional functional assay were in the same range as the activity levels of factors II, VII, IX, and X, whereas the fast functional test yielded significantly lower levels. The presented results indicate that very similar protein C levels were obtained with both functional and the immunologic assay except in patients under oral anticoagulation.

Adult↗
PubMed1988

Increased helper inducer and decreased suppressor inducer phenotypes in the rheumatoid joint.

Cells isolated from the joints of patients with rheumatoid arthritis (RA) exhibit functional immune abnormalities, such as diminished suppressor activity, depressed response to mitogens, and enhanced immunoglobulin production. We sought to characterize the T lymphocyte subsets in the synovial fluid (SF) and peripheral blood (PB) of RA patients in an attempt to clarify the mechanism(s) responsible for these functional immune abnormalities. We used dual-immunofluorescence staining techniques with several combinations of monoclonal antibodies, including anti-4B4 and anti-2H4, which define, respectively, the helper inducer and suppressor inducer subsets of CD4+ (Leu-3+ and T4+) cells. Mononuclear cells from normal PB (n = 9), RA PB (n = 6), and RA SF (n = 9) were analyzed, after staining, by flow cytometry. We observed a significant increase (P less than 0.0002) in the number of cells bearing the helper inducer phenotype (CD4+, 4B4+), and a significant decrease (P less than 0.0002) in the number of cells bearing the suppressor inducer phenotype (CD4+, 2H4+), in RA SF compared with the levels in PB from RA patients or normal control subjects. We also observed that the CD8+, 2H4+ subset was significantly decreased (P less than 0.0001) in SF compared with that in PB. There was no significant difference in the lymphocyte subset levels in PB from RA patients and from normal subjects. These observations may account, in part, for the reduced suppressor activity, the poor response to mitogens, and the autologous mixed lymphocyte reaction, as well as the enhanced production of Ig and rheumatoid factor, that are observed in the rheumatoid joint.

Arthritis, Rheumatoid↗
PubMed1988

CT scans and neuroleptic response in schizophrenia: a multidimensional approach.

Structural brain abnormalities in schizophrenia have been reported in a number of studies using computed tomography (CT). However, the prevalence and the localization of the abnormalities vary widely among studies. These discrepancies might stem from clinical and demographic differences among samples, from the choice of the CT parameters, or from the use of different criteria to define abnormalities. In an attempt to overcome these difficulties, we studied 12 CT parameters in 30 schizophrenic patients and 30 sex- and age-matched controls, and evaluated the data simultaneously through multidimensional scaling (MDS). MDS offers a graphic representation in which subtle deviations in the different CT parameters can be detected, independently of predetermined criteria for the definition of abnormalities. MDS distinguished 13 patients from the controls as having deviant values in one or more CT parameters. Five of these patients were first-onset schizophrenics. Patients with deviant CT parameters showed significantly poorer response to haloperidol therapy over 3 weeks than did patients without deviant CT parameters. Our results suggest that the MDS approach might be useful in identifying more precisely patients with and without structural brain abnormalities.

Adult↗
PubMed1988

Degradation and biological inactivation of thyrotropin releasing hormone (TRH): regulation of the membrane-bound TRH-degrading enzyme from rat anterior pituitary by estrogens and thyroid hormones.

Thyrotropin releasing hormone (TRH, pyroGlu-His-Pro-NH2) is important in the regulation of adenohypophyseal hormone secretion and also serves important functions in extrahypothalamic brain areas, indicating that it is involved in neurotransmission and other forms of cellular communication. This hypothesis is strengthened by the observation that TRH is rapidly inactivated by a heterogeneously distributed ecto-enzyme which exhibits a high degree of substrate specificity. Moreover, in the rat, the activity of the membrane-bound TRH-degrading enzyme of the anterior pituitary is found to be stringently controlled by thyroid hormones and estrogens. In contrast, the activity of the TRH-degrading brain enzyme is neither influenced by thyroid hormones nor estrogens. These data indicate that the TRH-degrading brain enzyme serves specialized functions for the transmission of TRH signals and apparently represents the peptidergic equivalent to acetylcholine esterase, whereas the membrane-bound adenohypophyseal TRH-degrading enzyme itself fulfills a biologically important control function within feedback-regulatory mechanisms.

Animals↗
PubMed1988

Histopathological and clinical correlations of cystosarcoma phyllodes.

We performed a detailed retrospective analysis of 25 patients treated primarily at Northwestern Memorial Hospital, Chicago, for cystosarcoma phyllodes. Histopathological evaluation correlated well with malignancy, but clinical suspicion did not. Pathological studies indicated that high-grade tumors, necrosis, infiltrating margin, and the presence of more than one mesenchymal element were often associated with aggressive behavior. Flow-cytometric analyses of DNA aneuploidy and proliferative index supported the grading system we used, since all four malignant cases examined showed high proliferative index, and three of the four cases showed aneuploidy. None of the low-grade cases, including the recurrent ones, showed increased proliferative index or aneuploidy. We believe that flow-cytometric analysis ought to be performed on cases in which there is doubt regarding the potential malignancy.

Adolescent↗
PubMed1987

Relationship between target cell cycle and susceptibility to natural killer lysis.

Studies from several laboratories have evaluated the role of cell surface antigenic molecules on target cells in natural killer (NK)-mediated cytotoxicity. A number of these cell surface molecules are associated with cell proliferation and may be expressed preferentially during one phase of the cell cycle. The purpose of this investigation was to evaluate the role that target cell cycle plays in susceptibility to NK lysis. Enrichment (greater than 80%) of cells from NK-resistant and NK-sensitive cell lines in the G0G1, S, and G2M phases of the cell cycle was achieved by centrifugal elutriation. We demonstrate that there was no influence of cell cycle on NK-mediated lysis of NK-resistant or susceptible cell lines.

Cell Cycle↗
PubMed1987

Induction of high-grade, high-stage carcinomas in the rat urinary bladder.

The hypothesis that biologic aggressiveness of bladder cancer is determined by carcinogen dose was tested using heterotopically transplanted rat urinary bladders (HTBs). Young male Fischer rats, which were recipients of normal bladders, were divided into three groups; the first group received 0.5 mg of N-methyl-N-nitrosourea (MNU) into HTBs for six doses, a second, 0.05 mg for six doses and the third, 1 mg for three doses. Separately, a group of animals received bladders from rats treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BHBN) in drinking water for 4 weeks; the transplanted bladders then were treated with 0.5 mg of MNU for six doses. Treatment with the larger dose of MNU resulted in a significant increase in tumor incidence and frequency of invasive carcinomas. The combination carcinogen treatment induced more invasive carcinomas than the single treatment. The data suggest that deeply invasive carcinomas may develop in two ways: the first is by emergence of a more anaplastic cell population within a pre-existing noninvasive carcinoma and the second is by the de novo development of an invasive carcinoma directly from a severely dysplastic urothelium, which is acceptable as carcinoma in situ. Squamous differentiation was characteristic of deeply invasive carcinomas. The dose of carcinogen(s) is a determinant of aggressiveness of bladder carcinomas.

Animals↗
PubMed1987

Blood-cerebrospinal fluid barrier in schizophrenic patients.

A total of 15 young white male patients newly diagnosed as schizophrenic (DMS III) were examined for signs of blood-cerebrospinal fluid (CSF) barrier alteration and CNS IgG synthesis. Of the 15 patients, 8 exhibited signs of increased blood-CSF barrier permeability. There was a high correlation between the ratio for CSF/serum albumin concentration and the CSF total protein concentration. Local IgG synthesis in the CNS was not detected in any of the patients.

Adult↗
PubMed1987

Peptide uptake by astroglia-rich brain cultures.

Uptake of carnosine has been investigated in astroglia-rich primary cultures derived from brains of newborn mice. It could be demonstrated that carnosine is not degraded by these cells but rapidly taken up in an energy- and sodium-dependent process. Uptake and release of carnosine by these cells were found to be mediated by a saturable, high-affinity transport system with apparent kinetic constants of Km = 50 microM and Vmax = 22.7 nmol X h-1 X mg protein-1. Uptake of carnosine is strongly inhibited by other dipeptides as well as by various oligopeptides, e.g., Leu-enkephalin. However, uptake of the radiolabeled tripeptide D-Ala-L-Ala-L-Ala was not observed. Radiolabeled Leu-enkephalin also did not accumulate intracellularly, even if degradation of the peptide was prevented by use of peptidase inhibitors. These results suggest that uptake of carnosine is catalyzed by a dipeptide-specific transport system with broad substrate specificity. With neuronal cells in primary culture, uptake of carnosine or other peptides was not observed.

Amino Acids↗
PubMed1987

Processing of the initiation methionine from proteins: properties of the Escherichia coli methionine aminopeptidase and its gene structure.

Methionine aminopeptidase (MAP) catalyzes the removal of amino-terminal methionine from proteins. The Escherichia coli map gene encoding this enzyme was cloned; it consists of 264 codons and encodes a monomeric enzyme of 29,333 daltons. In vitro analyses with purified enzyme indicated that MAP is a metallo-oligopeptidase with absolute specificity for the amino-terminal methionine. The methionine residues from the amino-terminal end of the recombinant proteins interleukin-2 (Met-Ala-Pro-IL-2) and ricin A (Met-Ile-Phe-ricin A) could be removed either in vitro with purified MAP enzyme or in vivo in MAP-hyperproducing strains of E. coli. In vitro analyses of the substrate preference of the E. coli MAP indicated that the residues adjacent to the initiation methionine could significantly influence the methionine cleavage process. This conclusion is consistent, in general, with the deduced specificity of the enzyme based on the analysis of known amino-terminal sequences of intracellular proteins (S. Tsunasawa, J. W. Stewart, and F. Sherman, J. Biol. Chem. 260:5382-5391, 1985).

Amino Acid Sequence↗