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Biomedical subjects

R Lohrmann

Publications and source records attributed to R Lohrmann.

At least 19 recordsLinked to original sources
PubMed1981

Condensation of activated diguanylates on a poly(C) template.

We have studied the metal-ion catalysis of a number of reactions of the isomers of ImpGpG on a poly(C) template. In the absence of a catalytic metal ion, oligomers at least up to (pG)20 are obtained from the ImpGpG isomers in a 1-methylimidazole buffer. The Pb2+ ion improves the yield of longer oligomers and changes substantially the distribution of linkage isomers. The Pb2+ ion greatly improves the yield of longer oligomers obtained from G and ImpGpG on a poly(C) template. The self-condensation of ImpGpG in a 2, 6-lutidine buffer is much less efficient than in a 1-methylimidazole buffer. The Zn2+ greatly increases the yield of products from the [3'-5']-linked dimer, but fails to catalyze the formation of long oligomers from the [2'-5']-linked dimer. The bonds formed in the Zn2+-catalyzed self-condensation of ImpG3pG on poly(C) are mainly [3'-5']-linked.

Guanine Nucleotides↗
PubMed1980

Efficient metal-ion catalyzed template-directed oligonucleotide synthesis.

The Pb2+ and Zn2+ ions are efficient catalysts for the polycytidylic acid-directed polymerization of an activated guanylic acid derivative, guanosine 5'-phosphorimidazolide. The products include oligomers of 30 to 40 units in length. The nucleotide residues are predominantly 2'-5' linked when Pb2+ is the catalyst, and predominantly 3'-5' linked in the presence of Zn2+. The significance of these results in the context of the prebiotic evolution of RNA polymerase is discussed.

DNA-Directed RNA Polymerases↗
PubMed1979

Studies of oligoadenylate formation on a poly (U) template.

We have studied a variety of condensation reactions involving poly (U) as template and isomeric adenosine dinucleotides as substrates. We find that [3'-5']-linked dinucleotides such as A3pA and pA3pA are better acceptors than the corresponding [2'-5']-linked compounds, while ImpA2pA is a better donor than ImpA3pA. The reaction between A2pA and ImpA3pA, for example, yields only 4% of product while the reaction of A3pA with ImpA2pA yields 86% of product. The more efficient condensation reactions of dimers are about as efficient as the self-condensation of ImpA. They yield a few percent of material in which five or more substrate molecules are linked together. The percentage of the natural [3'-5']-linkage in the product varies greatly, from as little as 1% to as much as 45%.

Chromatography, Paper↗
PubMed1979

Self-condensation of activated dinucleotides on polynucleotide templates with alternating sequences.

We have prepared substantial quantities of the alternating polymers poly(U-G) and poly(C-A) and have used them as templates for the self-condensation of ImpApC, ImpCpA, ImpGpU and ImpG. We find that the condensation of ImpGpU and ImpUpG on poly(C-A) is efficient, the condensation of ImpCpA on poly(U-G) is moderately efficient, while the condensation of ImpApC on poly(U-C) proceeds poorly. In many cases, the product is predominantly 3'-5'-linked. These reactions demonstrate unequivocally, for the first time, that template-directed reactions occur in double-helical structures. Furthermore, they describe for the first time a pair of reactions in which each of two complementary polymers facilitates the synthesis of the other. The prebiotic significance of these findings is discussed.

Chemical Phenomena↗
PubMed1979

Template-directed synthesis of oligoadenylates catalyzed by Pb2+ ions.

The Pb2+ ion is an effective catalyst for the template-directed condensation of ImpA on poly(U). This reaction generates up to 35% of oligomers 5 or more units long. Furthermore, the product is predominantly 3'-5'-linked (75%) unlike that from the uncatalyzed reaction which is more than 90% 2'-5'-linked. The significance of metal-ion catalysis for prebiotic polynucleotide formation is discussed.

Adenine Nucleotides↗
PubMed1978

Formation of the imidazolides of dinucleotides under potentially prebiotic conditions.

Imidazolides of dinucleotides such as ImpApA can be formed from the corresponding dinucleotides in a two-stage process, which gives up to 15% yields under potentially prebiotic conditions. First a solution of the dinucleotide and sodium trimetaphosphate is dried out at constant temperature and humidity. This produces polyphosphates such pnApA in excellent yield (greater than or equal to 80%). The products are dissolved in water, imidazole is added, and the solution is dried out again. This yields the 5'--phosphorimidazolides.

Humidity↗
PubMed1977

Formation of nucleoside 5'-phosphoramidates under potentially prebiological conditions.

Adenosine 5'-phosphoramidates form when solutions containing adenosine 5'-polyphosphates pnA (n greater than or equal to 3) or P1, P2-diadenosine 5'-diphosphate and amines are allowed to dry out. Mg ions catalyze these reactions. We have studied systems containing ammonia, imidazole, glycine, ethylenediamine and histamine. The yields of adenosine 5'-phosphoramidates range from 10-50% based on the nucleotide. The prebiotic significance of the reactions is discussed.

Adenosine Monophosphate↗
PubMed1977

Template-directed reactions of aminonucleosides.

We have studied the reactions between adenosine 5'-phosphorimidazolide and 9-(2-amino-2-deoxyxylofuranosyl) adenine (I) or 3'-methylamino-3'-deoxy-adenosine (II), both with and without a poly (U) template. We find that both amino compounds react much more rapidly than does adenosine, in the absence of a template. The rate of reaction is greatly enhanced by a poly (U) template in the case of I, but the enhancement is slight in the case of II.

Adenosine↗
PubMed1976

Formation of nucleoside 5'-polyphosphates under potentially prebiological conditions.

Aqueous solutions of linear inorganic polyphosphates incubated in presence of Mg ions depolymerize to give trimetaphosphate. The presence of a nucleoside 5'-phosphate has little influence upon the reaction. Drying the products obtained by incubating a linear polyphosphate with Mg ions in the presence of a nucleoside 5'-phosphate yields nucleoside 5'-polyphosphates. The prebiological relevance of the reactions is discussed.

Chemical Phenomena↗
PubMed1976

Polymerization of nucleotide analogues I: reaction of nucleoside 5'-phosphorimidazolides with 2'-amino-2'-deoxyuridine.

2'-Amino-2'-deoxyuridine reacts efficiently with nucleoside 5'-phosphorimidazolides in aqueous solution. The dinucleoside monophosphate analogues were obtained in yields exceeding 80% under conditions in which little reaction occurs with the natural nucleosides. In a similar way, the 5'-phosphorimidazolide of 2'-amino-2'-deoxyuridine undergoes self-condensation in aqueous solution to give a complex mixture of oligomers. The phosphoramidate bond in the dinucleoside monophosphate analogues is stable for several days at room temperature and pH 7. The mechanisms of their hydrolysis under acidic and alkaline conditions are described.

Deoxyuridine↗
PubMed1975

Formation of nucleoside 5'-polyphosphates from nucleotides and trimetaphosphate.

When solutions of nucleoside 5'-phosphates and trimetaphosphate are dried out at room temperature, nucleoside 5'-polyphosphates are formed. The Mg++ ion shows a superior catalytic function in this reaction when compared with other divalent metal ions. Starting with nucleoside 5'-phosphates, Mg++ and trimetaphosphate, the predominant products in the nucleoside 5'-polyphosphate series pnN are p4N, P7N and p10N. Nucleoside 5'-diphosphates yield p5N and p8N, nucleoside 5'-triphosphates give p6N and p9N. The prebiological relevance of these reactions is discussed.

Adenine Nucleotides↗
PubMed1975

Prebiotic peptide-formation in the solid state. II. Reaction of glycine with adenosine 5'-triphosphate and P1,P2-diadenosine-pyrophosphate.

When a solution containing gly-N-pa and imidazole is evaporated to dryness and then maintained at a temperature between 65 degrees C and 100 degrees C, high yields of AppA and obligoglycines are obtained. We believe that ImpA is formed first, and then activates the carboxyl group of glycine or gly-A-pA. If glycine, ATP or AppA, and imidazole are heated together in the solid state, ImpA is formed and ATP , or indirectly from imidazole and gly-N-pA. Next the carboxyl group or glycine is activated by the ImpA formed in situ. The subsequent reactions of activated glycine leads to the formation of oligoglycines and the 2' (3')-glycylester of pA. Under plausible prebiobic conditions, good yields of oligoglycines up to the octamer can be obtained from glycine, ATP and imidazole.

Adenosine Diphosphate↗
PubMed1975

Triple helices formed by polyuridylic acid with some adenosine derivatives.

We have prepared a variety of derivatives of adenosine which, at neutral pH's, carry protonated amine functions. These derivatives form stable helical structures with polyuridylic acid, but the melting points are not substantially higher than those of helical complexes formed by adenosine derivatives lacking cationic groups.

Adenosine↗
PubMed1975

Prebiotic peptide-formation in the solid state. I. Reactions of benzoate ion and glycine with adenosine 5'-phosphorimidazolide.

The reactions of benzoate ion and of glycine with adenosine 5-phosphorimidazolide have been investigated. Benzoate reacts first to give the anhydride, benzoyl-adenylate, which, in the presence of excess imidazole, reacts further to give the 2'- and 3'-esters of adenosine 5'-phosphate. Glycine also first attacks the imidazolide to give an anhydride, but this compound may react further either to give 2- and 3'-esters or to form peptides, depending on the reaction conditions.

Adenine Nucleotides↗