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Biomedical subjects

B M Olivera

Publications and source records attributed to B M Olivera.

At least 163 records · Page 9Linked to original sources
PubMed1981

The pyridine nucleotide cycle. Studies in Escherichia coli and the human cell line D98/AH2.

Different metabolic steps comprise the pyridine nucleotide cycles in Escherichia coli and in the human cell line HeLa D98/AH2. An analysis of the 32P-labeling patterns in vivo reveals that in E. coli, pyrophosphate bond cleavage of intracellular NAD predominates, while in the human cell line, cleavage of the nicotinamide ribose bond predominates. In E. coli, intracellular NAD is processed differently from extracellular NAD. Conversion of intracellular NAD to nicotinic acid mononucleotide (NaMN) can be demonstrated in intact cells. We have also assayed and purified an enzyme, NMN deamidase, which converts NMN to NaMN. These data suggest that in E. coli, the predominant intracellular pyridine nucleotide cycle operative under our experimental conditions is: NAD leads to NMN leads to NaMN leads to NaAD leads to NAD Thus, a metabolic event requiring pyrophosphate bond cleavage of NAD, such as DNA ligation, initiates most NAD turnover. In the human cell line, the data are consistent with the following NAD turnover cycle: (formula, see text) Whereas in E. coli, ADP-ribosylation does not make a quantitatively important contribution, we suggest that in HeLa cells, ADP-ribosylation events initiate NAD turnover.

Escherichia coli↗
PubMed1981

Peptide toxins from Conus geographus venom.

Three homologous toxic peptides which cause postsynaptic inhibition at the vertebrate neuromuscular junction have been purified from the venom of the marine snail Conus geographus. Their amino acid sequences are: (formula see text) The biologically active peptides are monomeric, with internal disulfide bonds.

Amino Acid Sequence↗
PubMed1980

NAD turnover in microplasmodia of physarum polycephalum.

The rate of NAD turnover in microplasmodia of Physarum polycephalum was investigated using a double labeling technique with (14C)-adenine or adenosine and (3H)-nicotinamide. The half-life of an NAD molecule in Physarum was estimated to be 25 min, which is shorter than in either E. coli or human cell lines. The half-life of NAD in the presence of an inhibitor of NADase and poly ADPR synthase, 5-methylnicotinamide, was also investigated, but found to be indistinguishable from controls. The possible reasons for this and for the rapid turnover is discussed in the light of the known functions for NAD in prokaryotes and eukaryotes.

NAD↗
PubMed1978

Processivity of DNA exonucleases.

A homopolymer system has been developed to examine the digestion strategies of DNA exonucleases. Escherichia coli exonuclease I and lambda-exonuclease, are processive enzymes. However, T7 exonuclease, spleen exonuclease, E. coli exonuclease III, the 3' leads to 5'-exonuclease of T4 DNA polymerase, and both the 3' leads to 5' and the 5' leads to 3' activity of E. coli DNA polymerase I dissociate frequently from the substrate during the course of digestion. Regions of duplex DNA are a dissociation signal for exonuclease I.

Animals↗
PubMed1978

DNA intermediates at the Escherichia coli replication fork: effect of dUTP.

We have directly tested the hypothesis that elevated levels of dUTP cause the formation of small DNA fragments at the replication fork of Escherichia coli. Addition of increasing levels of dUTP to lysates on cellophane discs results in an increasing number of strand scissions in the newly replicated DNA. Lysates of strains defective in dUTPase produce many more scissions at the same level of dUTP. The size distribution of Okazaki pieces obtained in vivo can be reconstituted in vitro on cellophane discs if appropriate levels of dUTP are present. Although uracil excision leads to the apparent production of Okazaki pieces from both daughter strands, DNA synthesis is actually asymmetric under these conditions. De novo chain initiation events occur on only one strand. It is suggested that asymmetry of synthesis in vivo may be masked by uracil excision and other postreplication processing mechanisms.

DNA Polymerase I↗
PubMed1976

Turnover at nicotinamide adenine dinucleotide in cultures of human cells.

The rate of turnover of nicotinamide adenine dinucleotide (NAD) in the human cell line, D98/AH2, has been estimated by measuring the rates of entry into and exit from NAD molecules of 14C-adenine. In one set of experiments, cells were labeled by growth in medium containing 14C-adenine for six hours and then shifted to medium without labeled adenine. The loss of 14C-adenine from the adenine nucleotide and pyridine nucleotide pools was measured, and the data were analyzed using an analytical treatment which corrects for the relatively slow turnover of precursor pools. The loss of 14C-adenine from the NAD pool and from the precursor ATP pool could be related to the absolute rate of NAD breakdown. Under the experimental conditions used, the rate of NAD turnover ranged from 83,000 to 126,000 molecules per second per cell. In a complementary experiment cells were grown in the presence of unlabeled adenine, then shifted into medium containing 14C-adenine and the rate of entry of 14C-adenine into adenine and pyridine nucleotides was measured. The data were treated using a similar analysis to relate the rate of entry of 14C-adenine into NAD and the precursor ATP pools to the absolute turnover rate of NAD. This analysis gave a value for NAD turnover of 78,000 molecules per second per cell in excellent agreement with results from the pulse-chase experiments. The results from both types of experiment indicate that within D98/AH2 cells the half-life of an intact NAD molecule is 60 +/- 18 minutes. Thus, in a human D98/AH2 cell growing with a generation time of 24 hours, NAD is turning over at twice the rate found in Escherichia coli with a generation time of half an hour.

Adenine↗
PubMed1976

Pyridine nucleotide metabolism in imaginal discs of Drosophila melanogaster.

The pyridine nucleotide metabolism of imaginal discs of Drosophila melanogaster has been studied in vitro by incubating discs with labeled nicotinic acid in the presence and absence of ecdysterone. The major labeled compounds found within the discs are NAD, NADP, and nicotinic acid. There is preferential uptake of nicotinamide over nicotinic acid, although the Priess-Handler pathway is used exclusively. The presence of ecdysterone produces a small increase in the NADP/NAD ratio, and an increase in NAD synthesis, probably to compensate for increased NAD turnover.

Animals↗