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Biomedical subjects

C Walter

Publications and source records attributed to C Walter.

At least 19 recordsLinked to original sources
PubMed1992

Characterization of site-directed mutations in conserved domains of MalK, a bacterial member of the ATP-binding cassette (ABC) family [corrected].

Site-directed mutagenesis was used to change four amino acid residues (Q82, P152, L179, H192) in the MalK subunit of S. typhimurium maltose transport system which are highly conserved among members of the ATP-binding cassette (ABC) family. Replacement of H192 caused complete failure to complement the transport defect of a malK strain whereas changes of the other residues resulted in reduced or wild-type activity. The purified mutant proteins exhibited ATPase activity comparable to wild-type MalK.

ATP-Binding Cassette Transporters↗
PubMed1992

Large scale purification, nucleotide binding properties, and ATPase activity of the MalK subunit of Salmonella typhimurium maltose transport complex.

The malK gene, encoding a membrane-associated component of the maltose transport complex of Salmonella typhimurium was cloned into an expression vector downstream of the promoters lambda pR and lambda pL and a strong translation initiation region. Escherichia coli strain JM109 harboring the resulting plasmid pCW14 synthesized a protein of apparent molecular mass of 43 kDa upon temperature shift, as demonstrated by sodium dodecyl sulfate-gel electrophoresis. The identity of the protein was determined by N-terminal amino acid sequencing. The overproduced protein was sequestered in inclusion bodies as revealed by electron microscopy. The protein was purified to homogeneity on a large scale by disrupting the cells with a passage through a Ribi press, solubilizing the inclusion bodies with urea, and subsequent chromatography on Red Agarose. Purified MalK, as the membrane-bound MalK protein could be covalently modified by [gamma-32P]8-azido-ATP. Furthermore, the purified protein bound [gamma-32P] ATP with a dissociation constant of 150 microM and exhibited ATPase activity, which was stimulated by dimethyl-sulfoxide and inhibited by ADP.

ATP-Binding Cassette Transporters↗
PubMed1992

High frequency, heat treatment-induced inactivation of the phosphinothricin resistance gene in transgenic single cell suspension cultures of Medicago sativa.

One descendant of the Medicago sativa Ra-3 transformant T304 was analysed with respect to the somatic stability of the synthetic phosphinothricin-N-acetyltransferase (pat) gene which was used as a selective marker and was under the control of the 5'/3' expression signals of the cauliflower mosaic virus (CaMV) gene VI. In order to quantify gene instability, we developed a system for culturing and regenerating individual cells. Single cell suspension cultures derived from T304 and the ancestral non-transgenic M. sativa cultivar Ra-3, were established. The cells were regenerated into monoclonal calli. In transgenic calli, the phosphinothricin (Pt)-resistance phenotype was retained after more than 2 months of non-selective growth. In contrast, up to 12% of the suspension culture cells grown under nonselective conditions and at constant temperature (25 degrees C) lost the herbicide-resistance phenotype within 150 days. Surprisingly, a heat treatment (37 degrees C), lasting for 10 days, during the culture period resulted in an almost complete (95%) loss of the Pt resistance of the suspension culture cells. However, the frequency of cell division was identical in cultures grown under normal and heat treatment conditions. A biochemical test revealed that no phosphinothricin-N-acetyltransferase activity was present in heat treated, Pt-sensitive cells. The resistance level of the Pt-sensitive transgenic cells was equivalent to that of the wild-type cells. A PCR analysis confirmed the presence of the pat gene in heat treated, Pt-sensitive cells. From these results it is concluded that the Pt resistance gene was heat-inactivated at a high frequency in the M. sativa suspension cultures.

Acetyltransferases↗
PubMed1992

Managing service change in post HIV drugs services--a case study from Inner London.

The advent of HIV/AIDS has presented a major ideological challenge to established drug treatment agencies, where the incorporation of HIV-prevention strategies has proved problematic. This case study analyses the response to the HIV/AIDS epidemic by the drug misuse services of one Inner London district health authority (Bloomsbury) during the period 1985-89. While innovation and enthusiasm were much in evidence, a number of special problems prevented an effective and coherent strategic response. Key factors in the management of change in drugs/HIV services are identified which may be of special importance to clinicians, managers and funders and a number of key organizational and managerial competencies are suggested.

HIV Infections↗
PubMed1991

Total avulsion of an osseointegrated screw.

The close union achieved between pure grade titanium and healthy bone makes dislocation a rare event. We report the case of the total avulsion of an apparently well-integrated implant from a healthy mastoid bone.

Adolescent↗
PubMed1991

A chimeric nucleotide-binding protein, encoded by a hisP-malK hybrid gene, is functional in maltose transport in Salmonella typhimurium.

We have isolated a hybrid gene, composed of the first 455 nucleotides of hisP and nucleotides 275-1107 of malK, the genes coding for the nucleotide-binding components of the high-affinity transport systems for histidine and maltose in Salmonella typhimurium, respectively. The fusion had occurred by recombination within 11 homologous base pairs located between the two DNA fragments. In the chimeric protein peptidic motifs A and B, proposed to be part of the nucleotide-binding fold, originate from HisP and MalK, respectively. Plasmid pES42-39, harbouring the hybrid gene, was shown to complement only a malK mutation but failed to complement a hisP deletion mutation. The chimeric protein was identified by immunoblotting as a protein with an apparent molecular mass of 49kDa. Removal of the C-terminal 77 amino acid residues from the chimeric protein resulted in the loss of function in transport. In contrast, 51 amino acid residues could be removed from the C-terminus of wild-type MalK without any effect. Upon overproduction the chimeric protein, as wild-type MalK, inhibited expression of the malB regulon. However, both truncated proteins, when overproduced, did not exhibit this activity. Based on these results, a tentative model of the functional domains of MalK is presented.

ATP-Binding Cassette Transporters↗
PubMed1991

Transmural gradient of adenosine in canine heart during functional hyperemia.

Effects of beta-adrenergic stimulation and atrial pacing on the transmural gradient of intracellular free adenosine were assessed in dog hearts in vivo by measurement of the accumulation of S-adenosylhomocysteine (SAH) in the presence of homocysteine (1.6 mg.kg-1.min-1 iv). Isoproterenol (0.3-0.5 micrograms.kg-1.min-1 iv for 30 min) consistently enhanced left ventricular dP/dtmax (86%), heart rate (38%), and myocardial oxygen consumption (MVO2; 62%) within 3 min while formation and release of adenosine transiently increased. Diastolic aortic pressure fell from 107 +/- 12 to 58 +/- 5 mmHg, and the transmural gradient of SAH was 1.6-, 2.5-, and 4.4-fold increased in subepi-, mid- myo-, and subendocardial layers, respectively. Adenosine formation was inversely related to diastolic aortic pressure. Maintaining aortic pressure greater than 65 mmHg only slightly enhanced venoarterial difference of adenosine despite a greater augmentation of MVO2. Pacing the heart at 209 +/- 4 beats/min enhanced MVO2 by 42% and increased subepi-, midmyo-, and subendocardial levels of SAH by 1.5-, 3.3- and 1.9-fold, respectively. These results demonstrate that in the in situ heart 1) beta-adrenergic stimulation and pacing cause an inhomogeneous transmural increase in free intracellular adenosine mainly affecting the subendocardial and midmyocardial layers; 2) diastolic aortic pressure as the driving force of coronary perfusion is of critical importance for cardiac adenosine formation; and 3) the kinetics of oxygen consumption and adenosine formation are clearly dissociated during beta-stimulation.

Adenosine↗
PubMed1991

[Croup and air pollutants: results of a two-year prospective longitudinal study].

The Reutlingen/Tübingen/Rottenburg region in Baden-Württemberg is characterized by medium and small sized towns and rural areas. In 1986/87 875 cases of croup were registered there by the treating physicians during a 24-months period. In consideration of meteorological and virological "disturbing variables" the influence of the measured air pollution by SO2, NO, NO2, CO, ozone and dust on croup frequency was computed by means of statistical regression methods. For the months September till March, the main manifestation period of croup, weak but statistically significant influences of the daily means of NO and NO2 were found, for the whole year influences of NO, NO2, and CO. During the winter months temperature correlates positively and velocity of wind negatively, both statistically with significance, to croup frequency. The essential conditions of croup are individual and familiar disposition on the one hand, virus infections on the other. Air pollution of a concentration like given in the investigated region was found to be a weak additional factor that favours the manifestation of croup.

Air Pollutants↗
PubMed1988

Hematopoietic growth factor glycosylation. Multiple forms of chicken myelomonocytic growth factor.

The production of chicken myelomonocytic growth factor (cMGF) can be rapidly induced by bacterial lipopolysaccharide from the macrophage cell line HD11. Immunoprecipitation analysis of lipopolysaccharide-induced HD11 cells labeled with various radioactive precursors showed the secretion of a variety of cMGF forms. The precursor-product relationships of the different cMGF forms were studied by pulse-chase experiments, by long-term metabolic labeling in the presence or absence of glycosylation- and oligosaccharide-processing inhibitors, as well as by glycosidase treatment of immunoprecipitates. Our results show that the half-time for intracellular processing/secretion is less than 10 min, making cMGF one of the most rapidly processed proteins. The different forms of the factor are generated from a 24-kDa polypeptide precursor by co- and post-translational acquisition of one or two N-linked oligosaccharides and by O-linked glycosylation. In addition, a fraction of cMGF is modified by long chain, chondroitinase-sensitive, sulfated glycans. This modification is tunicamycin-sensitive, suggesting that the sulfated glycans are attached to N-linked rather than to O-linked oligosaccharides.

Animals↗
PubMed1988

Pathogenic and non-pathogenic Entamoeba: pore formation and hemolytic activity.

Pore-forming activity in planar lipid bilayers and liposomes of extracts from differentially pathogenic Entamoeba and the capacity of trophozoites and subcellular fractions to lyse human red blood cells (hrbc) were investigated. In all amebas studied, the two activities paralleled each other. They were high in E. histolytica irrespective of the virulence of the particular strain, but low in non-pathogenic E. histolytica-like amebas of human origin as well as in E. invadens, which is pathogenic for reptiles, and in E. moshkovskii isolated from sewage. We conclude that the capacities to insert pores and to lyse are not sufficient for virulence although they may be necessary. The subcellular distribution of the hemolytic activity of E. histolytica and its sensitivity to a variety of inhibitors and activators differ from those of other known amebic cytotoxic activities including pore formation. Therefore, there may be an additional constituent of E. histolytica involved in the cytotoxicity of the parasite.

Animals↗