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Biomedical subjects

K Tsukada

Publications and source records attributed to K Tsukada.

At least 343 records · Page 19Linked to original sources
PubMed1978

Ribonuclease H activity in cultured plant cells.

Ribonuclease H (RNAase H) was extracted from cultured plant cells, strain GD-2 and characterized. RNAase H activity in logarithmical growing cells is much higher than that of stationary cells, and the response of RNAase H activity was very similar to that of DNA polymerase after culture. The activities of RNAase, DNAase, phosphodiesterase and alkaline phosphatase decrease parallel with the increase in growth, and increase to stationary phase, contrasting with those of DNA polymerase and RNAase H.

Cell Division↗
PubMed1977

Change of ribonuclease H activity in developing and regenerating rat liver.

Ribonuclease H (RNAase H), which specifically degrades RNA in RNA-DNA hybrids, has been studied with proliferating normal liver. Partial hepatectomy results in approximately two-fold increase of RNAase H activity in 24 h after 16 h lag phase in liver after operation. The activity of RNAase H as well as DNA ligase in the liver of newborn rats is high and the activities of both enzymes gradually decrease with same ratio during differentiation to low levels in the adult.

Aging↗
PubMed1977

Purification and properties of deoxyribonucleic acid ligases from rat liver.

DNA ligases have been purified 1,500-fold cytoplasmic fraction and 114-fold from 0.15 M NaCl extract of rat-liver nuclei. These enzymes catalyze the formation of a phosphodiester linkage between the 3'-hydroxyl group and the 5'-phosphoryl group of an interrupted strand in a DNA duplex. The enzyme from each fraction requires ATP and Mg2+ (or Mn2+) for activity, and its inhibited reversibly by p-chloromercuribenzoate. The cytoplasmic and nuclear enzymes are distinguished from each other by the following criteria: apparent molecular weight; sedimentation coefficient; charge properties; Km for Mg2+ (or Mn2+); Km for ATP; effect of ionic strength on the molecular and kinetic properties.

Adenosine Triphosphate↗
PubMed1977

Changes of DNA ligase in developing rat brain.

DNA ligase was isolated from rat brain and characterized. In developing rat brain the DNA ligase activities of the cerebellum increased after birth, at least 5 fold more than those of non-cerebellar parts. The DNA ligase activity in the cerebellum reached a maximum about 6 days after birth and then decreased towards maturation. The DNA ligase from the cerebellum can be fractionated into three molecular forms. Aging of the extracts leads to the conversion of the high molecular weight form into smaller weight forms.

Aging↗
PubMed1976

Amino acids and control of nucleolar size, the activity of RNA polymerase I, and DNA synthesis in liver.

The volume of nucleolar material per nucleus and the activity of RNA polymerase I (RNA nucleotidyltransferase I) become doubled in the liver cells of rats that are fed for several days a diet that lacks essential amino acids. Omission of methionine from a fully supplemented diet is equivalent to leaving out all the amino acids, and the responses to a deficiency of tryptophan are about 40% as great. Deprivation of one of the remaining essential amino acids gives either small responses or none at all. Supplementation of the methionine-free diet with cystine blocks the nucleolar enlargement and the enhancement of the polymerase activity that would otherwise take place, but the dispensable amino acid does not affect the responses to a deprivation of one of the other essential amino acids. After deprivation of all the essential amino acids or only methionine, hepatocytes make DNA when the rat is fed a meal with protein. A preparatory diet lacking in tryptophan is much less effective; a deficiency in any of the other indispensable compounds tested fails to prepare the liver for DNA synthesis. The results give hope that elucidation of the means by which methionine deprivation affects the nucleolus will also provide information on the regulation of nuclear DNA replication in liver. One attractive possibility is that the amino acid deficiency acts by producing some imbalance in protein metabolism.

Amino Acids↗
PubMed1975

Protein kinase in cultured plant cells.

A protein kinase (EC 2.7.1.37) which phosphorylates histones was purified partially from the soluble fractions of cultured plant cells. The optimum pH was 7.5 to 9.0. The activity wasnot stimulated by exogeneous cyclic AMP. It was thermolabile and completely dependent on the presence of Mg2+ or Mn2+ for activity. p-Chloromercuribenzoate inactivated this enzyme and this inactivation was overcome by mercaptoethanol.

Cyclic AMP↗
PubMed1975

Polynucleotide kinase from rat-liver nuclei. Purification and properties.

A polynucleotide kinase, which catalyzes the phosphorylation of 5'-hydroxyl ends of deoxyribonucleic acid in the presence of adenosine triphosphate, has been purified 260-fold with a yield of 14% from 0.15 M NaCl extracts of rat liver nuclei. The purified enzyme has a pH optimum of 5.5. The enzyme is reversible inhibited by p-chloromercuribenzoate. The S0.5 value (ligand concentration required for a half-maximal activity) for ATP is 2.5 muM. A bivalent cation is essential for the reaction and S0.5 values for Mg2+, Ca2+ and Mn2+ are 3.3 mM, 4 mM and 0.05 mM respectively. Pyrophosphate remarkable inhibits the activity with I0.5 value (ligand concentration required for a half-maximal inhibition) of 0.2 mM, and sulfate, with I0.5 of 0.5 mM, whereas phosphate weakly inhibits the activity with I0.5 of about 20 mM. An apparent molecular weight of the purified enzyme is estimated to be 8 X 10(4) by gel filtration on a column of Sephadex G-150, and the Stokes radius of the enzyme molecule is shown to be about 0.36 nm. Sucrose density gradient centrifugation reveals that the enzyme has a sedimentation coefficient of about 4.4 S.

Adenosine Triphosphate↗
PubMed1975

Cyclic adenosine 3':5'-monophosphate and the induction of deoxyribonucleic acid synthesis in liver.

A mixture containing glucagon and thyroid hormone was previously devised that enhances markedly nuclear DNA replication and mitosis in the parenchymal liver cells of the unoperated rat. It is now shown that the glucagon of the stimulatory solution can be completely replaced by a mixture of a butyryl derivative of cyclic adenosine 3':5'-monophosphate and theophylline. Cyclic guanosine 3':5'-monophosphate and its butyryl derivatives and insulin and high levels of glucose are inactive. The inactivity of N2-monobutyryl cyclic guanosine 3':5'-monophosphate cannot be ascribed to rapid breakdown in the animal or to the impenetrability of the liver cell since the coumpound elevates the rate of hepatic amino acid transport and the activity of ornithine decarboxylase. The observation of others (MacManus, J.P., Franks, D.J., Youdale, T. & Braceland, B.M. (1972) Biochem. Biophys. Res. Commun. 49, 1201-1207) that the level of cylcic adenosine 3':5'-monophosphate is raised during most of the prereplicative period after 70% hepatectomy is confirmed. The evidence supports a positive role for adenosine 3':5-monophosphate in regulating DNA synthesis in the liver.

Aminoisobutyric Acids↗