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Biomedical subjects

H G Klemperer

Publications and source records attributed to H G Klemperer.

13 recordsLinked to original sources
PubMed1971

Methylation of newly synthesized ribonucleic acid by isolated rat liver nuclei. Characterization of the ribonucleic acid synthesized by nuclei from starved animals.

1. Nuclei from rat liver incubated with S-adenosyl[methyl-(14)C]methionine incorporated radioactivity into RNA and into lipid and protein. 2. All of the labelled RNA was extracted from the nuclei with trichloroacetic acid at 90 degrees C. 3. The [(14)C]methyl-group incorporation into the hot-trichloroacetic acid extract was 30% inhibited by the addition of actinomycin D (100mug/mg of DNA) or by the omission of CTP, GTP and UTP. 4. Assuming that the main substrate for this triphosphate-dependent methylation was newly synthesized precursor rRNA containing one methyl group/30 uridylate residues, it was calculated that approx. 60% of the [(14)C]UMP incorporated under similar conditions represented precursor rRNA synthesis. 5. In agreement with this, low concentrations of actinomycin D (approx. 1mug/mg of DNA) sufficient to abolish the triphosphate-dependent incorporation of [(14)C]methyl group inhibited 68% of the [(14)C]UMP incorporation. 6. The incorporation of [(14)C]UMP by nuclei from starved animals decreased progressively with increasing periods of starvation, whereas the triphosphate-dependent [(14)C]methyl-group incorporation was not further decreased after 1 day of starvation. 7. This suggests that precursor rRNA synthesis decreased within 1 day whereas other species of RNA were affected only after longer periods of starvation.

Animals↗
PubMed1970

Decreased ribonucleic acid synthesis in isolated rat liver nuclei during starvation.

1. Isolated nuclei from starved rats showed a lowered incorporation of [(14)C]UMP into RNA. 2. The Mg(2+)-dependent incorporation was decreased by 30% after 1 day of starvation, but incorporation in the presence of Mn(2+) and ammonium sulphate decreased only after longer periods of starvation. 3. RNA synthesis by nuclei in the presence of excess of added RNA polymerase was unchanged after 1 day of starvation and was inhibited by 20% after 4 days. 4. The capacity of nuclei to bind actinomycin D was unchanged after 1 day and was decreased by 20% after 4 days of starvation.

Animals↗
PubMed1968

The phosphorylation of 5'-oligoadenylic acids by adenylate kinase and adenosine triphosphate.

1. Radioactivity was incorporated into 5'-O-phosphoryladenylyl-(3'-5')-adenosine (pApA) on incubation with adenylate kinase and [gamma-(32)P]ATP. The corresponding triadenylate and tetra-adenylate reacted more slowly. 2. Only oligoadenylate with a terminal 5'-phosphate served as the substrate. 3. The product formed from pApA was shown to behave like 5'-O-pyrophosphoryladenylyl-(3'-5')-adenosine (ppApA) on hydrolysis with alkaline phosphatase, potassium hydroxide and hydrochloric acid. 4. The characteristics of the reaction indicated that it was catalysed by adenylate kinase, but the rate of phosphate transfer from ATP to pApA was about 0.01% of that in the typical reaction with AMP. 5. The reverse reaction between ADP and ppApA occurred readily, but no additional phosphorylation of ppApA (to give pppApA) could be demonstrated.

Adenine Nucleotides↗
PubMed1968

Thymidine kinase in rat liver during development.

1. The activity of thymidine kinase in rat liver supernatant decreased with development to a value in the adult that was 1% of that in the 17-day foetus. 2. The foetal enzyme was more stable than the adult to gel filtration on Sephadex G-25 at 0 degrees . 3. The greater stability of the foetal enzyme to incubation at 45 degrees was attributable to the presence of higher concentrations of nucleotides in foetal liver supernatant. 4. The K(m) values for foetal and adult enzymes were approx. 2.5mum- and 2.1mum-thymidine respectively. 5. The foetal enzyme was more sensitive to inhibition by thymidine triphosphate. 6. The decline in enzyme activity during the neonatal period was correlated with a shift in the enzyme properties from the foetal to the adult type, and may reflect the decrease in the proportion of haemopoietic tissue in the liver.

Age Factors↗
PubMed1967

The incorporation of cytidine 5'-monophosphate and other ribonucleotides by an enzyme preparation from rat-liver microsomes.

1. An enzyme preparation from rat-liver microsomes incorporated all four ribonucleotides from the corresponding triphosphates into ribosomal RNA. The reaction was Mn(2+)-dependent, but UMP incorporation also occurred in the presence of Mg(2+). 2. The incorporation of any one ribonucleotide was inhibited by the presence of the other three ribonucleoside triphosphates and by denatured DNA. 3. The product of the reaction consisted of short chains of homopolymer attached to the primer ribosomal RNA. 4. ;Soluble' RNA, synthetic polyribonucleotides, and oligoribonucleotides were also effective primers for CMP incorporation. 5. When phosphodiesterase-treated ;soluble' RNA was the primer, CMP was incorporated into positions usually occupied by the normal terminal trinucleotide sequence of intact ;soluble' RNA, but the enzyme did not synthesize a specific terminal sequence consisting of a defined number of CMP residues.

Adenosine Triphosphate↗
PubMed1967

Altered specificity of transfer-ribonucleic acid nucleotidyltransferase in the presence of manganese.

1. s-RNA nucleotidyltransferase incorporated CMP into phosphodiesterase-treated s-RNA more rapidly in the presence of Mg(2+) (10mm) than in the presence of Mn(2+) (2mm). UMP was incorporated more rapidly in the presence of Mn(2+), and at high ionic strength the incorporation of CMP was also more rapid in the presence of Mn(2+). 2. The capacity of phosphodiesterase-treated s-RNA for CMP, UMP and AMP was increased in the presence of Mn(2+). Terminal sequences of more than one UMP or AMP residue were synthesized, but these atypical reactions were inhibited when CTP was added. CMP was incorporated rapidly to form -pCpC terminal sequences and then more slowly as longer chains were formed, but very little CMP was incorporated into s-RNA-pCpCpA. 3. CMP was incorporated into phosphodiesterase-treated 5s RNA and ribosomal RNA to form short chains of polyC attached to the primer RNA. This reaction was inhibited by the presence of s-RNA. 4. A small Mn(2+)-dependent incorporation of CMP was also primed by poly(A).(U) and poly(C).(I).

Adenine Nucleotides↗