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Biomedical subjects

T Koch

Publications and source records attributed to T Koch.

At least 253 records · Page 14Linked to original sources
PubMed1983

Acridine-psoralen amines and their interaction with deoxyribonucleic acid.

A series of novel compounds in which a 9-acridinyl nucleus is linked to a psoralen nucleus in the 5- or 8-position via polyamines was prepared and examined. Their reversible binding to DNA and their irreversible binding to DNA and DNA cross-linking upon irradiation with UV-A light were examined. It was found that they were all less efficiently photoreactive than 8-methoxypsoralen (8-MOP), both in cross-linking and photobinding to DNA, whereas the ratio between their photobinding and cross-linking was 40-400 times that of 8-MOP. Compounds in which the linker was attached to the 5-position in psoralen showed smaller cross-linking and photobinding efficiencies and larger ratios between photobinding and cross-linking than those of psoralens attached in the 8-position. This strongly indicates that the 9-substituents of the acridines are oriented toward the minor groove. Flow linear dichroism studies showed that the compounds were DNA intercalating with the acridine moiety, whereas the psoralen moiety in no case was clearly intercalating. This conclusion was further supported by viscometry which also strongly indicated monointercalation.

Acridines↗
PubMed1979

Infective substructures of measles virus from acutely and persistently infected cells.

Ribonucleoprotein from cells acutely or persistently infected with measles virus were shown to be infectious by the calcium phosphate technique. Very little or no infectivity was obtained when calcium phosphate precipitation was omitted. Electron microscopy showed that the majority of ribonucleoprotein structures isolated from acutely infected cells were folded, whereas those from persistently infected cells were linear in appearance.

Animals↗
PubMed1978

Schwann cell abnormalities in 2,5-hexanedione neuropathy.

Distinctive cytoplasmic alterations of Schwann cells were observed by electron microscopy in rats and mice with peripheral neuropathy induced by chronic exposure to 2,5-hexanedione. Pronounced enlargement of Schwann cells was due to accumulation of 100 angstrom cytoplasmic filaments and endoplasmic reticulum and was most often observed after 12--15 weeks exposure to 2,5-hexanedione. Examination of teased nerve fibres revealed segmental demyelination and remyelination involving axons of normal diameter as well as giant axons. The filament disorder induced by 2,5-hexanedione administration is not limited solely to axoplasmic contents. Possible mechanisms of demyelination are discussed and the changes are compared to those observed in human neuropathy for which 2,5-hexanedione appears to be the closest experimental model.

Animals↗
PubMed1977

Giant axonal neuropathy: a childhood disorder of microfilaments.

A sural nerve biopsy was performed on an 8-year-old boy with a chronic, slowly progressive polyneuropathy. Light and electron microscopy as well as teased nerve-fiber preparations demonstrated numerous giant axons filled with closely packed neurofilaments. Both myelinated and unmyelinated fibers were involved. Segmental demyelination, remyelination, and onion-bulb formation by multiple Schwann cell processes were observed, suggesting recurrent Schwann cell dysfunction. Abundant aggregates of cytoplasmic microfilaments occurred in Schwann cells, endothelial cells, perineurial cells, endoneurial fibroblasts, and endomysial fibroblasts. These findings support the proposal that giant axonal neuropathy is a generalized disorder of cytoplasmic microfilaments and that segmental demyelination occurs concomitantly with axonal and Schwann cell disease. The pathogenesis of this rare disorder is discussed with reference to experimental toxic neuropathies.

Axons↗
PubMedDate not supplied

In vivo 1H, 31P-[1H] and 13C-[1H] magnetic resonance spectroscopy of malignant histiocytoma and skeletal muscle tissue in man.

Human tumor and skeletal muscle tissue was studied by means of in vivo 1H, 31P, and 13C MRS. The examinations were performed with a 1.5 T whole-body MR scanner equipped with a second RF system. Localized 1H and broadband proton-decoupled 31P and 13C MR spectra were obtained in measurement times of 5, 10 and 33 min, respectively, from a malignant fibrous histiocytoma in a patient and from gastrocnemius muscle tissue in healthy volunteers. Proton decoupling enhanced the sensitivity (via the nuclear Overhauser effect) and the information available from in vivo 31P and 13C MR spectra significantly. The most information was obtained from 1H-decoupled 31P spectra. Observation of more than one spin species allows peak assignments to be verified mutually. The spectral data of the histiocytoma differ largely from that of muscle tissue and show a tumor with elevated pH value, normal level of nucleoside 5'-triphosphates, and high level of compounds involved in phospholipid turnover. The multinuclear in vivo MRS experiment may allow the non-invasive observation of almost the complete pathway of phospholipid synthesis and degradation in intact human tissue.

Histiocytoma, Benign Fibrous↗
PubMedDate not supplied

Solid-phase synthesis of peptide nucleic acids.

Peptide nucleic acids (PNA) were synthesized by a modified Merrifield method using several improvements. Activation by O-[benzotriazol-1-yl]-1,1,3,3-tetramethyluronium hexafluorophosphate in combination with in situ neutralization of the resin allowed efficient coupling of all four Boc-protected PNA monomers within 30 min. HPLC analysis of the crude product obtained from a fully automated synthesis of the model PNA oligomer H-CGGACTAAGTCCATTGC-Gly-NH2, indicated an average yield per synthetic cycle of 97.1%. N1-benzyloxycarbonyl-N6(3)-methylimidazole triflate substantially outperformed acetic anhydride as a capping reagent. The resin-bound PNAs were successfully cleaved by the 'low-high' trifluoromethanesulphonic acid procedure.

Base Sequence↗
PubMedDate not supplied

Photochemical immobilization of anthraquinone conjugated oligonucleotides and PCR amplicons on solid surfaces.

Ligand immobilization on solid surfaces is an essential step in fields such as diagnostics, bio sensor manufacturing, and new material sciences in general. In this paper a photochemical approach based on anthraquinone as the chromophore is presented. Photochemical procedures offer special advantages as they are able to generate highly reactive species in an orientation specific manner. As presented here, anthraquinone (AQ) mediated covalent DNA immobilization appears to be superior to currently known procedures. A synthetic procedure providing AQ-phosphoramidites is presented. These reagents facilitate AQ conjugation during routine DNA synthesis, thus enabling the AQ-oligonucleotides to be immobilized in a very convenient and efficient manner. AQ-conjugated PCR primers can be used directly in PCR. When the PCR is performed in solution, the amplicons can be immobilized after the PCR. Moreover, when the primers are immobilized prior to the PCR, a solid-phase PCR can be performed and the amplicons are thus produced directly on the solid support.

Anthraquinones↗
PubMedDate not supplied

The oxidative cleavability of protein cross-linking reagents containing organoselenium bridges.

The intensive use of cleavable cross-linking reagents to study macromolecular biological interactions has shown a demand for optimizing these reagents in such a way that the involved macromolecules remain intact. The present work focuses on the development of selenium linkers that are cleavable by mild oxidation. The efficiency of cross-linking and subsequent cross-linker cleavage with a new series of such homo- or heterobifunctional cross-linking reagents have been tested in a simple model system, consisting of albumin and cytochrome c. Resultant, or residual, covalent complex formation is examined by SDS-polyacrylamide gel electrophoresis. From this work it can be concluded that diallyl selenides are readily cleaved by mild oxidation, whereas dialkyl selenides and benzyl alkyl selenides can only be cleaved when the alkyl part of the selenide has an electron-withdrawing group next to the beta-carbon from selenium.

Animals↗
PubMedDate not supplied

Photolytic cleavage of DNA by nitrobenzamido ligands linked to 9-aminoacridines gives DNA polymerase substrates in a wavelength-dependent reaction.

A series of reagents containing 3- or 4-nitrobenzamido ligands tethered to 9-aminoacridine via variable-length linkers have been prepared and their properties as photochemical DNA cleavers (photonucleases) examined. When irradiated with approximately 300-nm light, where the nitrobenzamido ligand can absorb, they cleave DNA in an oxygen-independent reaction presumably involving oxygen transfer from the nitro group to the deoxyribose units of the DNA backbone (Nielsen et al., 1988b). This reaction is pH independent and only slightly affected by the linker length, and the DNA fragments are not substrates for DNA polymerase. When approximately 420-nm light is used, were only the 9-aminoacridinyl ligands absorb, the DNA cleavage is also oxygen-independent but pH dependent, requires DNA saturation with the reagent (base pair:reagent less than or equal to 2), and is most efficient with the longer linkers. The cleavage is specific for guanine residues and results in 5'-phosphate termini and heterogeneous (more than four products) 3'-termini. One of the products is presumably 3'-hydroxy since DNA photocleaved with nitrobenzamido acridine reagents and 420-nm radiation are substrates for DNA polymerase in a nick translation assay as well as for the Klenow fragment. An electron-transfer mechanism is suggested.

Aminoacridines↗
PubMedDate not supplied

Pitfalls in characterization of protein interactions using radioiodinated crosslinking reagents. Preparation and testing of a novel photochemical 125I-label transfer reagent.

Much attention has been focused on the study of protein interactions with radioiodinated photo-crosslinking reagents, and pitfalls in using this methodology are discussed. A new photochemical and cleavable heterobifunctional crosslinking reagent, succinimidyl N-14-(2-hydroxybenzoyl)-N-11-(4-azidobenzoyl)-9-oxo-8,11,14-triaza -4,5- dithiatetradecanoate (SHAD) was prepared, and its potential as a label transfer reagent was tested in model systems. SHAD was radioiodinated, and the labeled reagent (125I-SHAD) was converted to an amide (125I-HADM, as a mimicry of conjugation to protein 1) and photolyzed. When compared to the widely used SASD reagent (sulfosuccinimidyl 2-[[(4-azidosalicyl)-amino]ethyl]-1,3- dithiopropionate, Pierce), SHAD has a number of decisive advantages. The amide of 125I-SASD (125I-ASDM) was generated and photolyzed, and it was found that at least 50% of the radioactivity is released from 125I-ASDM after 3 min of irradiation, whereas only approximately 10% is liberated from 125I-HADM under similar conditions. Furthermore, 125I-HADM was photolyzed in the presence of excess amine (mimicry of crosslinking to protein 2), and the product was cleaved by reduction (mimicry of label transfer). The transformations in the course of photolysis were monitored by UV spectroscopy and TLC analysis, and a high degree of reagent cleavage upon reduction was demonstrated. 125I-SHAD was used to crosslink Lys78-plasminogen and fibrin. 125I-SHAD was conjugated to Lys78-plasminogen in the dark. Fibrinogen and thrombin were added, and Lys78-plasminogen was crosslinked to the fibrin clot by exposure to light.(ABSTRACT TRUNCATED AT 250 WORDS)

Azides↗