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T Ooka

Publications and source records attributed to T Ooka.

At least 91 records · Page 5Linked to original sources
PubMed1979

Characterization of an Epstein-Barr virus-induced DNA polymerase.

The addition of iododeoxyuridine to P3HR-I cell cultures led to a large increase in both Epstein-Barr virus (EBV)-induced DNA polymerase activity and early antigen-positive cells. This EBV-induced DNA polymerase was separated from the cellular alpha- and beta-polymerases by sequential column chromatography on Sepharose 6B, DEAE-cellulose, and phosphocellulose, resulting in partial purification of about 320-fold. The partially purified-EBV DNA polymerase could be distinguished from the cellular DNA polymerases by its activation by salts, its catalytic properties, and its degree of sensitivity to N-ethylmaleimide, phosphonoacetic acid, araATP, and araCTP. The viral polymerase showed properteis similar to those reported for other herpesvirus DNA polymerases. The enzyme exhibited optimal activity for copying activated calf DNA in the presence of 50 mH (NH4)2SO4 and was resistant to 150 mM (NH4)2SO4. It utilized with high efficiency template-primer poly(dC)-oligo(dG)12-18 or poly(dA)-oligo(dT)12-18, but failed to copy poly(rA)-oligo(dT)10 and oligo(dT)10, indicating that this enzyme has characters distinct from DNA polymerase gamma, reverse transcriptase, and terminal deoxynucleotidyl transferase. Phosphonacetic acid inhibited not only EBV DNA polymerase, but also, to a lesser degree, the cellular polymerase alpha. AraATP did not severely inhibit viral activity, whereas the polymerase alpha was inhibited most effectively. Both EBV polymerase and polymerase alpha were inhibited at a comparable level by araCTP.

Ammonium Sulfate↗
PubMed1976

Structural and membrane modifying properties of suzukacillin, a peptide antibiotic related to alamethicin. Part A. Sequence and conformation.

The primary structure and conformation of the polypeptide antibiotic suzukacillin A are investigated. Suzukacillin A is isolated from the Trichoderma viride strain 1037 and exhibits membrane modifying and lysing properties similar to those of alamethicin. A combined gas chromatographic mass spectrometric analysis of the trifluoroacetylated peptide methyl esters of partial hydrolysates revealed a tentative sequence of 23 residues including 10 2-methylalanines and one phenylalaninol, which shows many fragments known from alamethicin: Ac-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-Gln-Aib-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-Glu(Pheol)-Gln-OH. All chiral amino acids and phenylalainol have L-configuration. Ultraviolet and infrared spectroscopy, circular dichroism in various solvents and in particular 13C nuclear magnetic resonance have been used for a comparative study of suzukacillin with alamethicin. Suzukacillin has a partially alpha-helical structure and the helix content increases largely from polar to lipophilic solvents. Suzukacillin aggregates more strongly than alamethicin in aqueous medis due to a longer alpha-helical part and higher number of aliphatic residues. A part of the alpha-helix is exceptionally stabilized due to 2-methylalanine residues shielding the peptide bonds from interactions with polar solvents. In lipophilic solvents and lecithin vesicles particularly large temperature induced reductions of the high alpha-helix content are found for alamethicin. Suzukacillin shows similar temperature coefficients in lipophilic media, however, in contrast to alamethicin a more linear change in intensity of the Cotton effects is observed.

Alamethicin↗
PubMed1976

Structural and membrane modifying porperties of suzukacillin, a peptide antibiotic related to alamethicin. Part B. Pore formation in black lipid films.

Suzukacillin, a polypeptide consisting of presumably 23 amino acids and 1 phenylalaninol, is produced by a Trichoderma viride strain No. 1037 and it can be isolated from the culture medium. It shows membrane-modifying properties similar to those of alamethicin. Discrete condustance fluctuations indicate the formation of oligomer pores of varying diameter. On the basis of voltage jump relaxation experiments evidence is given that the dimer is the nucleation state from which pore formation starts and the oligomer disappears. According to the voltage-current characteristics, voltage-dependent and voltage-independent conductances are observed. A slow process is involved, which can be interpreted as a change in the equilibrium distribution between different conformations of the suzukacillin monomer at the membrane interphase. This change results from its interaction with the lipid matrix. Differences in experimental observations between suzukacillin and alamethicin are attributed to the relatively larger alpha-helix and higher number of aliphatic side chains of the suzukacillin monomer and to a more intense interaction with the lipid membrane. This leads to a higher probability of forming dimers from monomers and to the occurrence of "inactivation".

Alamethicin↗
PubMed1975

Studies on changes in DNA polymerase activity during the cell cycle in synchronized KB cells.

We have demonstrated the presence of two DNA polymerases in KB cells and studied the variation of their activities in a synchronous cell population. During the cell cycle we observed in nuclei, only one DNA dependent DNA polymerase, the 3.4 S or minipolymerase, and similarly in the cytoplasm only one enzyme, the 8.3 S or maxipolymerase. The former shows preference for native DNA and the latter for denatured DNA. Their Mg++ and K+ requirements are different and their pH optima are 8.5 and 7 for nuclear polymerase and cytoplasmic polymerase respectively. The cytoplasmic polymerase activity remains stable from one cell cycle to the other with each cell reconstituting its stock at the start of the following cycle (G1 and early S phases). On the contrary nuclear activity decreases in G2, M and early G1, then increases to a maximum in the middle of the S phase. This fluctuation in enzyme activity could be due to degradation, transfer to the cytoplasm or the association of the enzyme with the chromatin and/or the nuclear membrane after completion of DNA synthesis. Our results do not permit us to choose between these three hypotheses. However their significance is discussed in the light of the results obtained by some authors who, on the contrary, have tended to minimise the role of the minipolymerase in DNA duplication, whereas we, from our findings, ascribe a preponderant role to this enzyme. The cytoplasmic maxipolymerase (8.3 S) may simply be a storage form of the enzyme from which minipolymerase can be formed as needed.

Animals↗