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Biomedical subjects

K H Scheit

Publications and source records attributed to K H Scheit.

At least 109 records · Page 6Linked to original sources
PubMed1975

Hydrogen bonding abilities of 2,4-dithiouridine derivatives.

The base pairing ability of a di-2,4-thiouridine derivative was studied in carbon tetrachloride solutions by the methods of infrared spectroscopy. The strength of the association by hydrogen bonding was found to decrease in the following order: adenine-uracil, adenine-di-2,4-thiouracil, uracil-uracil, and di-2,4-thiouracil-di-2,4-thiouracil. These findings contrast with the previously demonstrated fact that poly(s2s4U) is strongly self-associated and does not form a complex with poly(A). To correlate these results, it is proposed that long range stabilizing forces are acting between the di-2,4-thiouracil residues in polynucleotide chains. This assumption also explains the existence of an ordered structure in the alternating copolymer poly(s2s4U-A).

Adenine Nucleotides↗
PubMed1975

The effects of thioketo substitution upon uracil-adenine interactions in polyribonucleotides. Synthesis and properties of the alternating polynucleotides poly(r(A-s2U)) and poly(r(A-s2s4U)).

The polynucleotides poly[r(A-s-2U)] and poly]r(A-s2s4U)] have been synthesized and characterized by nearest-neighbour analysis, sedimentation analysis as well as spectroscopic techniques. Absorption-temperature profile and absorption-pH profile of poly[r(A-s-2U)] did not reveal a structural transition between 10 and 95 degrees C even at low ionic strength, although a variety of properties indicated a helical structure of poly[r(A-s-2U)]: remarkable hyperchromicity of the absorption spectrum, circular dichroic spectrum displaying extrema of large amplitudes, resistance against hydrolysis by ribonuclease and interaction with ethidium bromide in a manner which is characteristic of helical polynucleotides. Our results show that interactions of the type A-s-2U and A-s-2s-4U do in fact exist in helical polynucleotides. The properties of poly]r(As-2U)] furthermore demonstrate the general stabilizing effect of 2-thioketopyrimidine bases in helical polynucleotides by virtue of vertical stacking interactions with neighbouring pyrimiding and purine bases.

Circular Dichroism↗
PubMed1975

Properties of ATP and UTP analogues with P-S-C-5' bonds.

Analogues of ATP and UTP bearing C-5'-S-P ester bonds were found not to be substrates but weak competitive inhibitors of Escherichia coli RNA polymerase. The K-i values of the analogues obtained in the transcription of poly[d(A-T)] or poly(dT) under various conditions are in the order of millimolar. Evidence was derived from proton magnetic resonance spectra that nucleotides with C-5'-S-P bonds do not exist in gauche-gauche conformation normally adopted by natural occurring nucleotides. This leads us to assume that the gauche-gauche conformation is an essental prerequisite for substrates of RNA polymerase. Ado-5'-S-PPP substituted for ATP as substrate of hexokinase from yeast rather effectively thus indicating that a distinct stereochemical orientation of the alpha-phosphate ester bond is not a stringent requirement for substrates of this enzyme.

Adenosine Triphosphate↗