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Biomedical subjects

T Ramakrishnan

Publications and source records attributed to T Ramakrishnan.

At least 37 records · Page 2Linked to original sources
PubMed1978

Effect of isonicotinic acid hydrazide-copper complex on Rous sarcoma virus and its genome RNA.

The copper complex of the antituberculous drug, insonicotinic acid hydrazide (INH), inhibits the RNA-dependent DNA polymerase of Rous sarcoma virus and inactivates its ability to malignantly transform chick embryo cells. The INH-copper complex binds to the 70S genome RNA of Rous sarcoma virus (RSV), which may account for its ability to inhibit the RNA-dependent DNA polymerase. The complex binds RNA more effectively than DNA in contrast to M-IBT-copper complexes, which bind both types of nucleic acids equally. The homopolymers, poly rA and poly rU, are bound by the INH-copper complex to a greater extent than poly rC. Isonicotinic acid hydrazide alone and CuSO4 alone bind neither DNA, RNA, poly (rA), poly (rU), nor poly (rC). However, CuSO4 alone binds poly (rI); INH alone does not. In addition to viral DNA synthesis, chick-embryo cell DNA synthesis is inhibited by the INH-copper complex. The extent of inhibition of cellular DNA synthesis is greater than that of cellular RNA and protein synthesis. No selective inhibition of transformation in cells previously infected with Rous sarcoma virus is observed.

Avian Sarcoma Viruses↗
PubMed1977

Inactivation and inhibition of Rous sarcoma virus by copper-binding ligands: thiosemicarbazones, 8-hydroxyquinolines, and isonicotinic acid hydrazide.

We have shown that three types of copper-binding ligands, thiosemicarbazones, 8-hydroxyquinolines, and isonicotinic acid hydrazide and their copper complexes, inactivate the transforming ability of RSV and inhibit its RNA-dependent DNA polymerases. Three other compounds, 2-pyridine thiosemicarbazone, 1-formyl isoquinoline thiosemicarbazone, and diphenyl thiocarbazone inhibit transformation by RSV intracellularly. Most but not all of these compounds bind to nucleic acids in the presence of copper, which may be important in their mode of action.

Avian Sarcoma Viruses↗
PubMed1977

Rate of ribonucleic acid chain growth in Mycobacterium tuberculosis H37Rv.

Two methods were employed to measure the rate of ribonucleic acid (RNA) chain growth in vivo in Mycobacterium tuberculosis H37Rv cultures growing in Sauton medium at 37 degrees C, with a generation time of 10 h. In the first, the bacteria were allowed to assimilate [3H]uracil or [3H]guanine into their RNA for short time periods. The RNA was then extracted and hydrolyzed with alkali, and the radioactivity in the resulting nucleotides and nucleosides was measured. The data obtained by this method allowed the calculation of the individual nucleotide step times during the growth of RNA chains, from which the average rate of RNA chain elongation was estimated to be about 4 nucleotides per s. The second method employed the antibiotic rifampin, which specifically inhibits the initiation of RNA synthesis without interfering with the elongation and completion of nascent RNA chains. Usint this method, the transcription time of the 16S, 23S, and 5S ribosomal RNA genes was estimated to be 7.6 min, which corresponds to a ribosomal RNA chain growth rate of 10 nucleotides per s.

Kinetics↗
PubMed1976

Purification and properties of DNA-dependent RNA polymerase from Mycobacterium tuberculosis H37RV.

RNA polymerase (nucleosidetriphosphate: RNA nucleotidyltransferase DNA-dependent), EC 2.7.7.6) was purified approximately 200 fold from Mycobacterium tuberculosis H37RV cells. The purified enzyme has a molecular weight of about 330 000-350 000 and is composed of four subunits. The subunits beta', beta and sigma have molecular weights different from those of Escherichia coli polymerase; the fourth, alpha subunit has a similar weight. The purified enzyme is a thousand-fold more sensitive to rifampicin, a potent antitubercular drug than the E. coli RNA polymerase, probably because of the difference in the beta subunits. This, with other data presented in this paper, indicate that the RNA polymerase of M. tuberculosis differs in its properties from that of E. coli.

Antitubercular Agents↗
PubMed1975

The purification and properties of peroxidase in Mycobacterium tuberculosis H37Rv and its possible role in the mechanism of action of isonicotinic acid hydrazide.

Peroxidase from Mycobacterium tuberculosis H37Rv was purified to homogeneity. The homogeneous protein exhibits catalase and Y (Youatt's)-enzyme activities in addition to peroxidase activity. Further confirmation that the three activities are due to a single enzyme was accomplished by other criteria, such as differential thermal inactivation, sensitivity to different inhibitors, and co-purification. The Y enzyme (peroxidase) was separated from NADase (NAD+ glycohydrolase) inhibitor by gel filtration on Sephadex G-200. The molecular weights of peroxidase and NADase inhibitor, as determined by gel filtration, are 240000 and 98000 respectively. The Y enzyme shows two Km values for both isoniazid (isonicotinic acid hydrazide) and NAD at low and high concentrations. Analysis of the data by Hill plots revealed that the enzyme has one binding site at lower substrate concentrations and more than one at higher substrate concentration. The enzyme contains 6g-atoms of iron/mol. Highly purified preparations of peroxidases from different sources catalyse the Y-enzyme reaction, suggesting that the nature of the reaction may be a peroxidatic oxidation of isoniazid. Moreover, the Y-enzyme reaction is enhanced by O2. Isoniazid-resistant mutants do not exhibit Y-enzyme, peroxidase or catalase activities, and do not take up isoniazid. The Y-enzyme reaction is therefore implicated in the uptake of the drug.

Catalase↗
PubMed1973

Protein synthesis in Mycobacterium tuberculosis H37Rv and the effect of streptomycin in streptomycin-susceptible and -resistant strains.

An efficient in vitro amino acid-incorporating system from Mycobacterium tuberculosis H37Rv was standardized. Ribonucleic acid (RNA) isolated from phage-infected M. smegmatis cells served as natural messenger RNA and directed the incorporation of (14)C-amino acids into protein. The effects of various antitubercular drugs and "known inhibitors" of protein synthesis on amino acid incorporation were studied. Antibiotics like chloramphenicol and tetracycline inhibited mycobacterial protein synthesis, though they failed to prevent the growth of the organism. This failure was shown to be due to the impermeability of mycobacteria to these drugs by use of "membrane-active" agents along with the antibiotics in growth inhibition studies. Several independent streptomycin-resistant mutants of M. tuberculosis H37Rv were isolated. Streptomycin inhibited the incorporation of (14)C-amino acids into proteins by whole cells of a streptomycin-susceptible strain by more than 90%, whereas very little or no inhibition was observed in either high-level or low-level streptomycin-resistant strains. In vitro, streptomycin was an effective inhibitor of susceptible strains, whereas in streptomycin-resistant strains the concentration of streptomycin at which half-maximal inhibition was produced varied according to the resistance of whole cells, and there was a correlation between the two. In one low-level streptomycin-resistant mutant, the in vitro amino acid-incorporating system was as sensitive to various concentrations of streptomycin as the parental type, and a possible involvement of a membrane site in the development of low-level resistance was indicated. Streptomycin susceptibility and high-level resistance were shown to be ribosomal in nature.

Antitubercular Agents↗