Search PubMed⌕ Search

Biomedical subjects

A Klein

Publications and source records attributed to A Klein.

At least 199 records · Page 11Linked to original sources
PubMed1994

9-O-acetylated sialic acids have widespread but selective expression: analysis using a chimeric dual-function probe derived from influenza C hemagglutinin-esterase.

While 9-O-acetylation of sialic acids has been reported in some mammalian tissues, the distribution of this modification on specific cell types and molecules is largely unknown. The influenza C virus hemagglutinin-esterase is a membrane-bound glycoprotein that binds specifically to 9-O-acetylated sialic acids (hemagglutinin activity) and then hydrolyzes the O-acetyl group (receptor-destroying activity). A recombinant soluble form of influenza C virus hemagglutinin-esterase wherein the C-terminal transmembrane and cytoplasmic domains are replaced by the Fc portion of human IgG retains both its recognition and enzymatic functions. The latter activity can selectively remove 9-O-acetyl groups from bound or free sialic acids and, under specific conditions, 7-O-acetyl groups as well. Irreversible inactivation of the esterase unmasks stable recognition activity, giving a molecule that binds specifically to 9-O-acetylated sialic acids. These probes demonstrate widespread but selective expression of 9-O-acetylated sialic acids in certain cell types of rat tissues. Patterns of polarized or gradient expression further demonstrate the regulated nature of this modification. Direct probing of blots and thin-layer plates shows selective expression of 9-O-acetylation on certain glycoproteins and glycolipids in such tissues. Thus, 9-O-acetylation is more widespread than previously thought and occurs on specific molecules and cell types.

Animals↗
PubMed1994

B-cell malignancy after low grade T-cell lymphoma.

BACKGROUND: Low grade, small lymphocytic, non-Hodgkin's lymphoma, was diagnosed in a 38-year-old woman. Thirty months after the initial diagnosis was made, a population of lymphoid cells with pathologic morphology was found in the patient's peripheral blood (PB). Cell phenotyping was performed and monoclonality was analyzed in cells obtained from a removed lymph node (LN) and the PB of the patient. METHODS: The cell phenotype was examined with immunofluorescence techniques using antibodies against SIg and monoclonal antibodies against CD1, CD3, CD4, CD5, CD8, CD19, and the kappa, and lambda light chains. Gene rearrangement analysis for monoclonality determination was performed with restricted DNA (EcoRI, Hin-dIII and BamHI) hybridized with either 32P-labeled T-cell receptor DNA probe (TcR-beta) or immunoglobulin-heavy chain probe (JH). RESULTS: With regard to the cell population of the removed LN, cell phenotyping showed the predominance of CD4+ T-cells over a polyclonal B-cell population. Gene rearrangement analysis proved the monoclonal nature of the T-cells and the polyclonal nature of the B-cells. As to the PB, gene rearrangement and cell phenotyping of the lymphocytes showed the predominance of monoclonal kappa type B-cells over polyclonal T-cells. CONCLUSIONS: The data obtained suggest two unrelated lymphoproliferative diseases in this patient, expressed as monoclonal T-cell population in LN and as monoclonal B-cell population in PB.

Adult↗
PubMed1994

Intracellular trafficking of glycosphingolipids: role of sphingolipid activator proteins in the topology of endocytosis and lysosomal digestion.

Glycosphingolipids (GSL) are components of the outer leaflet of the plasma membrane (PM) of vertebrate tissues. Our current knowledge of GSL metabolism and their intracellular traffic has been derived from metabolic studies but the exact mechanisms by which GSLs are transported from sites of synthesis (endoplasmic reticulum and Golgi) to the sites of residence (PM) and degradation (lysosomes) have not been clearly defined. It is now established that components of the PM reach the lysosomal compartment mainly by endocytic membrane flow. According to a new model, GSLs derived from the PM are thought to end up in intra-endosomal vesicles which could be delivered, by successive processes of membrane fission and fusion, along the endocytic pathway directly into the lumen of the lysosomes. Here the GSLs are degraded in a step-wise manner by exohydrolases. However, the catabolism of membrane-bound GSLs with short hydrophilic head groups needs the assistance of sphingolipid activator proteins (SAPs), which lift the GSLs from the plane of the membrane and present them for degradation to the lysosomal exohydrolases, which are usually water-soluble. The inherited deficiency of one of these enzymes or SAPs causes the lysosomal storage of their respective GSL substrates. In the case of the simultaneous deficiency of all 4 different SAPs the storage of all GSLs with short hydrophilic head groups occurs within multivesicular bodies and/or intra-lysosomal vesicles.

Cell Membrane↗
PubMed1994

Sphingolipid activator protein D (sap-D) stimulates the lysosomal degradation of ceramide in vivo.

Glycosphingolipids of cultured fibroblasts from patients with total sphingolipid activator proteins (SAPs) deficiency (Schnabel et al. J. Biol. Chem. 267:3312-3315, 1992) were labeled biosynthetically with [14C]serine. After a chase period of 120h the patients' fibroblasts showed increased labeling of ceramide, glucosylceramide, lactosylceramide and ganglioside GM3 in comparison to normal control cells. Addition of sap-D to the chase-media of the patients' fibroblasts led to the degradation of the accumulated ceramide down to nearly normal levels, whereas the levels of other labeled sphingolipids remained unaffected. In contrast, addition of sap-B to the chase-media of the patients' fibroblasts did not reduce the increased ceramide levels but resulted, as expected from in vitro experiments, in a specific decrease of levels of lactosylceramide and ganglioside GM3. Therefore, we conclude that sap-D stimulates in vivo the lysosomal degradation of ceramide.

Cells, Cultured↗
PubMed1994

Structure and expression of two plant genes encoding chromoplast-specific proteins: occurrence of partially spliced transcripts.

The genes encoding fibrillin and capsanthin-capsorubin synthase are specifically expressed during fruit ripening in Capsicum annuum, leading to the accumulation of these two proteins in chromoplasts. Here, we report for the first time the cloning of genomic DNA fragments encoding these two enzymes, as well as DNA fragments containing upstream regions which are potentially involved in the regulation of the expression of these genes. While the capsanthin-capsorubin synthase gene is uninterrupted, the fibrillin gene is interrupted by two introns, the first one being inefficiently spliced. Occurrence of unspliced transcripts is apparently not related to a post-transcriptional mechanism controlling the synthesis of fibrillin or an alternative polypeptide. This work provides tools for studies on gene activation and intron splicing in plants.

Amino Acid Sequence↗
PubMed1994

Quantitative discrimination of hepatic reticuloendothelial clearance and phagocytic killing.

An in vivo assay to quantify simultaneously two important components of hepatic reticuloendothelial system (RES) function--clearance and phagocytic killing--was developed in the rat. Intravenously injected E. coli labeled with Na51Cr and 5-[125I]-iodo-2'-deoxyuridine were cleared rapidly from the blood primarily by the liver. While hepatic 51Cr levels remained stable for 24 h following inoculation and provided a reliable measurement of clearance, hepatic 125I decreased over time. Hepatic 125I, calculated by sampling whole liver homogenates, accurately reflects the number of viable bacteria recovered from quantitative cultures of the same homogenates, thus validating this assay as a measure of bacteria killing. Pre-treatment of rats with substances previously shown to affect RES function (gadolinium, zymosan, and sheep erythrocytes) were found to selectively modulate clearance and/or killing. The correlation between hepatic isotope levels and viable hepatic bacteria, the gold standard for assessing the capacity of the liver to remove organisms from the blood and kill them, was preserved under conditions of up- and down-regulation of RES function. The ability to quantitatively discriminate two distinct components of the hepatic RES should provide a useful tool for future investigations of altered RES function.

Animals↗
PubMed1994

Selenium is involved in the negative regulation of the expression of selenium-free [NiFe] hydrogenases in Methanococcus voltae.

Competitive polymerase chain reactions (PCR) were used to analyze quantitatively the transcription patterns of the four different gene groups encoding [NiFe] hydrogenases in Methanococcus voltae. In cells growing in the presence of selenium, transcripts of only two of the hydrogenase transcription units could be detected in quantities above background levels. The missing transcripts encode the selenium-free F420-non-reducing and F420-reducing hydrogenases. In cells grown without selenium these transcripts are detectable, indicating the involvement of selenium in their transcriptional regulation.

Base Sequence↗
PubMed1994

An XRF study of trace elements accumulation in kidneys of tumor-bearing mice after treatment with cis-DDP with and without selenite and selenocistamine.

The effect of cis-DDP treatment with and without selenite and selenocistamine was studied on kidneys of tumor-bearing mice. The amounts of cis-DDP, selenite, and selenocistamine injected were chosen so as to be compatible with the treatment of humans. The animals were sacrificed at 7, 14, and 28 d after treatment. The kidneys were removed and subjected to trace element analysis by a novel X-ray fluorescence (XRF) method and for pathological assessment. The results show that following treatment with cis-DDP, K, Fe, Cu, and Zn reach a maximum level after 7 d; K, Fe, and Cu levels were significantly reduced by the addition of selenite. The level of Zn was reduced only in groups treated with selenite whereas that of K and Cu was reduced also in groups treated with selenocistamine with and without cis-DDP. The greatest increase in Pt and Se levels was reached 1 wk after injection with cis-DDP, with and without selenocompounds, and in the case of Pt was partly reduced by addition of selenite. Se returned to control values 2 wk after injection, although Pt was still high in all groups 2 and 4 wk after injection. The results corroborate the findings of our previous studies. The effect of selenocistamine in cis-DDP treated mice was partly insufficient. The pathological examination of the kidneys did not show any differences in the effect of various additives during the study.

Animals↗
PubMed1994

Lincomycin and spectinomycin in the treatment of breeding rams with semen contaminated with ureaplasmas.

Ureaplasma species were isolated from semen samples collected sequentially from one Awassi and three Assaf breeding rams. Each ram was injected subcutaneously with an aqueous solution of lincomycin and spectinomycin for five consecutive days at a dose equivalent to 4.5 mg kg-1 lincomycin and 9.0 mg kg-1 spectinomycin daily. Serum and semen samples were collected at intervals during the treatment and assayed for lincomycin. No Ureaplasma species were isolated from semen samples collected during the course of the treatment and at intervals for 17 days after the last treatment. The concentration of lincomycin in semen ranged from 0.51 microgram ml-1 four hours after treatment to 0.08 microgram ml-1 24 hours after treatment, and these levels were three to nine times higher than the corresponding serum concentrations.

Animals↗
PubMed1994

A new percutaneous technique for establishing venous bypass access in orthotopic liver transplantation.

Partial veno-venous bypass (VVB) is commonly used in orthotopic liver transplantation (OLT). Venous access for blood return during VVB classically uses a surgical cutdown on the left axillary vein (LAV), which may prolong operating time and can be associated with significant complications. The authors have developed an alternative means of establishing venous access whereby the anesthesia team places 8.5F venous cannulae preoperatively in one or two vessels (internal jugular, antecubital, or subclavian) percutaneously using the Seldinger technique. These cannulae then serve to accept venous return from below the diaphragm via a centrifugal pump. The aim fo the present study was to compare the hemodynamic profiles obtained during the anhepatic phase of OLT in patients in whom either a conventional LAV catheter (group 1) or percutaneous catheters (group 2) were used for return flow from a centrifugal pump. There were no identifiable complications related to venous access in either group of patients. Total operating room time was 800 +/- 30 minutes in group 1 and 720 +/- 40 minutes in group 2 (P = 0.17). Hemodynamic parameters were determined from continuous strip chart recordings of arterial, right atrial, and inferior vena caval (IVCP) pressures. Cardiac output (CO) was measured by thermodilution whereas pump flow was determined by an electromagnetic probe. Renal perfusion pressure (RPP) was calculated as the difference between mean arterial pressure (MAP) and IVCP. Bypass pump flow was greater, but not significantly different between group 1 (3.0 +/- 0.2 L/min) and group 2 (2.4 +/- 0.2 L/min) (P = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Axillary Vein↗
PubMed1994

Natural ligands of the B cell adhesion molecule CD22 beta can be masked by 9-O-acetylation of sialic acids.

CD22 beta is a B cell-restricted phosphoprotein expressed on the surface of mature resting B cells. It mediates interactions with other cells partly or exclusively via recognition of alpha 2-6-linked sialic acids on glycoconjugates. The sialylated N-linked oligosaccharides recognized best by CD22 beta are common to many glycoproteins, suggesting that additional regulatory mechanisms may exist. Since the exocyclic side chain of sialic acid is required for recognition, we explored the effects of a naturally occurring modification of the side chain, 9-O-acetylation. Semisynthetic N-linked oligosaccharides terminating with 9-O-acetylated, alpha 2-6-linked sialic acids showed markedly reduced binding to CD22 beta relative to their non-O-acetylated counterparts. Murine lymphoid cells were probed for natural CD22 beta ligands that might be O-acetylated using recombinant soluble forms of CD22 beta (CD22 beta Rg) and influenza C esterase (CHE-Fc, which specifically removes 9-O-acetyl esters from sialic acids). By flow cytometry analysis, CD22 beta Rg binding to splenic B cells and a subset of T cells was increased by pretreatment with CHE-Fc, indicating that some potential CD22 beta ligands are naturally "masked" by 9-O-acetylation. Unmasking of these CD22 beta ligands by removal of 9-O-acetyl esters from intact splenocytes substantially increases their CD22 beta-dependent adhesion in an in vitro adhesion assay. Probing of murine lymphoid tissue sections by CD22 beta Rg and CHE-Fc treatment demonstrates regionally restricted and differentially expressed patterns of distribution between masked and unmasked ligands. For example, lymph node-associated follicular B cells express high levels of CD22 beta ligands, none of which are masked by 9-O-acetylation. In contrast, the ligands on lymph node-associated dendritic cells are almost completely masked by 9-O-acetylation, suggesting that masking may regulate interactions between CD22 beta-positive B cells and dendritic cells. In the thymus, only medullary cells express CD22 beta ligands, and a significant portion of these are masked by 9-O-acetylation, particularly at the cortical-medullary junction. Thus, 9-O-acetylation of sialic acids on immune cells is in a position to negatively regulate CD22 beta adhesion events in a manner depending on both cell type and tissue localization.

Acetylation↗
PubMed1994

Adenylylsulphate reductase from the sulphate-reducing archaeon Archaeoglobus fulgidus: cloning and characterization of the genes and comparison of the enzyme with other iron-sulphur flavoproteins.

Adenylylsulphate (adenosine-5'-phosphosulphate, APS) reductase from the extremely thermophilic sulphate-reducing archaeon Archaeoglobus fulgidus is an iron-sulphur flavoprotein containing one non-covalently bound flavin group, eight non-haem iron and six labile sulphide atoms per molecule. Reevaluation of the enzyme structure revealed the presence of two different subunits with molecular masses of 80 and 18.5 kDa. The subunits are arranged in an alpha 2 beta subunit structure. We have cloned and sequenced a 2.7 kb segment of DNA containing the genes for the alpha and beta subunits, which we designate aprA and aprB, respectively. The two genes are separated by 17 bp and localized in the order aprBA. While a putative promoter could not be identified in the vicinity of aprBA a probable termination signal was found just downstream of the translation stop codon of aprA. The codon usage for aprBA shows strong preferences for G and C in the third codon position. aprA encodes a 73.3 kDa polypeptide, which shows significant overall similarities with the flavoprotein subunits of the succinate dehydrogenases from Escherichia coli and Bacillus subtilis and the corresponding flavoprotein of E. coli fumarate reductase. Part of the homologous peptide stretches could be assigned to domains that are involved in the binding of the substrate or of the FAD prosthetic group. aprB encodes a 17.1 kDa polypeptide representing an iron-sulphur protein, seven cysteine residues of which are arranged in two clusters typical of ligands of the iron-sulphur centres in ([Fe3S4][Fe4S4]) 7-Fe ferredoxins.

Amino Acid Sequence↗