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Biomedical subjects

K Tsukada

Publications and source records attributed to K Tsukada.

At least 325 records · Page 18Linked to original sources
PubMed1981

Characterization of DNA kinase from calf thymus.

DNA kinase has been purified to homogeneity from calf thymus. The purified enzyme, with a specific activity of 16.7 units/mg protein at 25 degrees C, exhibited a sharp pH/activity curve with a pH optimum at 5.5 and low activity at alkaline pH. The molecular weight of the enzyme was estimated by dodecylsulfate/polyacrylamide gel electrophoresis to be 5.4 X 10(4). The enzyme has a sedimentation coefficient of 4.0 S. An apparent molecular weight of 5.6 X 10(4) and a Stokes' radius of 3.3 nm were estimated by gel-filtration on Sephadex G-100. The enzyme phosphorylates neither yeast RNA nor poly(A) instead of DNA. Compared with rat liver DNA kinase, calf thymus DNA kinase is relatively resistant to the inhibition by sulfate (Ki = 7 mM) and pyrophosphate (Ki = 5 mM). The enzyme activity is markedly stimulated by polyamines at the sub-optimal concentration of Mg2+ but not by monovalent cations.

Animals↗
PubMed1981

Increased activity of a neutral protease in cytosol from rat hepatoma induced by N-2-fluorenylacetamide.

A protease active with N-alpha-benzoyl-DL-arginine-p-nitroanilide with an optimum pH of 7.3 has been found in the cytosol of rat liver. The activity of this protease increased in N-2-fluorenylacetamide-induced hepatoma as well as in fetal liver. It has been purified from normal liver and hepatoma about 200-fold. Its molecular weight is estimated by gel filtration to be about 200,000 in each tissue. The protease activity is unaffected by chymostatin, pepstatin, soybean trypsin inhibitor, and p-chloromercuribenzoate. Antipain, leupeptin, tosyl-L-lysine chloromethyl ketone, and phenylmethylsulfonyl fluoride inhibit the protease activity. This protease appears to be a serine protease.

2-Acetylaminofluorene↗
PubMed1980

Developmental changes of two distinct ribonuclease H activities from rat brain and characterization of these enzymes.

The specific activities of both Mg2+- and Mn2+-dependent ribonucleases H (RNAase H) from rat cerebella increased up to approx. the 6th day after birth and then decreased in adult rats. Those isolated from the non-cerebellar part decreased gradually toward adult levels after birth. The two enzymes could be separated by phosphocellulose chromatography. They can be distinguished from one another by their ionic requirement, molecular weight, sedimentation coefficient, optimal pH, sensitivity to the -SH reagent, and the effects of salt, polyamine and pyrophosphate. Both enzymes liberate a mixture of oligonucleotides from RAN substrates, with 5'-phosphate and 3'-hydroxyl termini.

Aging↗
PubMed1980

A protease from rat intestine.

Partially purified ribonuclease H from rat liver nuclei can be inactivated by a soluble fraction from rat intestine; this inactivation is restored by adding trypsin inhibitor, suggesting that the factor is a protease. A preparation has been isolated and purified to homogeneity. The molecular weight of the enzyme was estimated as 28 000 with an optimum pH of 8.0 and an isoelectric point at pH 4.5--4.7. The inactivating and proteolytic activities were observed in parallel throughout the purification procedures. Diisopropylphosphorofluoridate inhibited the protease activity. The protease inactivates deoxyribonuclease I, pyruvate kinase, and aldolase. From experiments with protease modifiers, it seems to be a serine protease of a trypsin-like nature.

Animals↗
PubMed1980

Changes in patterns of S-adenosylmethionine synthetases in fetal and postnatal rat liver.

Three isozymes of S-adenosylmethionine synthetase have been measured in the livers of rats from fetal life to maturity. A greater part of gamma-type enzyme is shown to be present in fetus and is joined by alpha- and beta-types during development. The amount of beta-type enzyme activated by dimethyl sulfoxide is very low in the fetus and rises sharply until about the 15th day after birth. The alpha-type enzyme appears after birth and increases in amount to the tenth day.

Age Factors↗
PubMed1979

Characterization of alkaline nuclease from rat liver mitochondria.

The alkaline nuclease (pH optimum 9.0) has been purified about 500-fold in 25% yield from the extract of rat liver mitochondria. The enzyme cleaves yeast RNA, poly(U), poly(U), poly(C) and denatured DNA to yield oligonucleotides with 5'-phosphoryl and 3'-hydroxyl ends. The enzyme has a molecular weight of about 60 000, a sedimentation coefficient of 4 S and an isoelectric point of 9.0. The behaviors of RNAase activity of the nuclease are identical with those of DNAase activity in column chromatography as well as in catalytic nature. The affinities of RNAase activity for substrate, Mg2+, spermidine and polyvinyl sulfate are lower than those of DNAase activity. The alkaline nuclease activity measured in the homogenate of regenerating rat liver is not significantly changed.

Animals↗
PubMed1979

Evidence for a single species of DNA ligase localized in nuclei of rat liver.

DNA ligase activity was distributed mainly in the extract of nuclei rapidly isolated from rat liver and about 20% of the nuclear activity in the cytoplasmic fraction. The DNA ligases of nuclear extract and cytoplasmic fraction showed similar gel-filtration patterns and the same sedimentation coefficient of 5.5 S. The appearance of 4-S enzyme from nuclei or nuclear extract was partly inhibited by phenylmethylsulfonyl fluoride. These results suggest that the major activity of DNA ligase in rat liver is due to a single species of the enzyme localized in nuclei and that 4-S nuclear DNA ligase reported previously is an artifact arising from 5.5-S enzyme during the isolation procedure.

Animals↗
PubMed1979

Multiple forms of ribonuclease H from rat liver cytosol.

Three forms (termed I, II, and III) of ribonuclease H (RNase H) [EC 3.1.4.34] activity are present in rat liver cytosol. These enzymes degrade RNA specifically in RNA-DNA hybrid structures. They were eluted at 0 M, 0.25 M, and 0.5 M KCl in phosphocellulose chromatography, and were further purified by using blue Sepharose. They are further distinguished from one another by their ionic requirements, optimal pH, molecular weights, sedimentation coefficients, and sensitivity to the -SH reagent, p-chloromercuribenzoate, although I and III have similar characteristics. They liberate a mixture of oligonucleotides with 5'-phosphate and 3'-hydroxyl termini.

Animals↗
PubMed1979

Two ribonucleases H from cultured plant cells.

Two forms of enzyme with ribonuclease H (RNase H) [EC 3.1.4.34] activities, have been partially purified from cultured plant cells, strain GD-2, derived from carrot root. One is an Mn2+-dependent RNase H, and the second is an Mg2+-dependent RNase H. These enzymes degrade RNA specifically in RNA-DNA hybrid structures. They were eluted at around 0.2 M and 0.4 M potassium chloride in phosphocellulose chromatography, and were further purified using blue Sepharose. Mg2+-dependent RNase H exhibits maximal activity at pH 9.0, and requires 10 to 15 mM Mg2+ for maximal activity, whereas the Mn2+-dependent enzyme is most active at pH 8.0, is maximally active at an Mn2+ concentration of 0.4 mM, and has some activity with Mg2+. Both enzymes require a sulfhydryl reagent for maximal activity. The enzymes liberate a mixture of oligonucleotides with 5'-phosphate and 3'-hydroxyl termini. The apparent molecular weight of the Mg2+-dependent RNase H was estimated to 18--20 X 10(4) and that of the Mn 2+- dependent RNase H was estimated to be 14 x 10(4) by gel filtration.

Cells, Cultured↗