Biomedical subjects

E Richet

Publications and source records attributed to E Richet.

25 records · Page 2Linked to original sources

PubMed1985

[Endocrine responses to insulin and gestational age in the calf].

The influence of hypoglycemia on pituitary and cortical and medullary adrenal response was studied in Holstein X Friesian male calves by giving an intravenous injection of bovine insulin (0.2 U/kg b.w.). Seventeen (9 treated and 8 control) calves were born spontaneously at term (278 days) and 9 (5 treated and 4 control) were delivered by caesarean section on day 260 of gestation. Insulin injections were given 1, 5, 10 and 30 days after birth. Plasma insulin and ACTH concentrations were measured by radioimmunoassay, cortisol by competitive protein binding assay, catecholamines by radio-enzymology and glucose by colorimetry (glucose oxydase). In calves born spontaneously at term, the insulin injection induced a significant rise in plasma ACTH and cortisol concentrations on day 5 after birth; this rise occurred on days 10 and 30 after birth in calves delivered on day 260 of gestation. The rise in plasma insulin concentration following insulin injection was always more pronounced and sustained in calves delivered before term than in those born spontaneously at term. Following insulin injection, plasma epinephrine concentration increased significantly only on day 30 in calves born spontaneously at term. After treatment, no other change in plasma catecholamine concentrations was observed in any group of calves at any age. These results indicate that the pituitary-adrenal axis responded similarly in 5-day old calves born spontaneously at term and in 10 (or 30)-day old calves delivered by caesarean section 18 days before the expected time of parturition.

Adrenocorticotropic Hormone↗

PubMed1984

Lambda integrative recombination: supercoiling, synapsis, and strand exchange.

We have presented the first results of three ongoing experiments on the biochemical mechanism of lambda site-specific recombination. First, we have shown that under the tension induced by negative supercoiling, a segment of attP and attR undergoes a transition to a novel conformation. The basis for detecting this new structure implies that it contains unpaired bases, perhaps arising as a result of the transition of an inverted repeat to a cruciform structure. Since the segment undergoing transition lies outside the homologous core region, the unpairing of DNA that we have detected cannot be directly involved in synapsis. It will be of interest to learn whether recombination proteins alter this conformational change, possibly to extend its effect into the core region. Second, we have demonstrated that replacing phosphate groups in attachment site DNA with phosphorothioates interferes with recombination. Our first experiments indicate that the effect depends on locating phosphorothioates precisely at the site of recombination crossover. We take this to mean that interference is primarily at the step of breakage and reunion; we plan to exploit this inhibition in an attempt to trap synaptic intermediates in recombination. Finally, we have found that the rare cleavage of attP DNA by Int can involve either one or both strands of the duplex. This indicates that the degree of coordination between Int action at the two halves of the core region can be variable. Although we do not know whether this variability affects binding of Int, breakage of DNA, or resealing of broken strands, our data suggest that this variability can be regulated by sulfhydryl reagents.

Bacteriophage lambda↗

PubMed1983

Escherichia coli uvrD mutants with thermosensitive DNA-dependent adenosine triphosphatase I (helicase II).

Three mutants producing thermosensitive DNA-dependent Adenosine triphosphatase (ATPase) I were screened from a collection of temperature-sensitive mutants of Escherichia coli K12. ATPase I purified to near homogeneity from one of the mutants (JE11000) possesses both thermosensitive DNA-dependent ATPase and DNA helicase activities. We have shown that ATPase I is encoded by the uvrD gene as first suggested by Oeda et al. (1982): (i) the thermosensitive ATPase I mutation present in JE11040 lies in or very close to the uvrD gene, (ii) ATPase I activity is absent in uvrD210, uvrD156, and uvrD252 mutants. Thus the thermosensitive mutations correspond to new uvrD mutations. However, the mutation present in JE11040 confers neither UV sensitivity nor mutator phenotype at high temperature. Evidence is presented that the mutant ATPase I is stabilized in vivo at 42 degrees C.

Adenosine Triphosphatases↗

PubMed1982

ACTH and plasma corticosteroid levels in young calves.

1. Plasma sodium, potassium, aldosterone and cortisol levels were measured in seven 11-day-old calves after ACTH infusion and in five control animals. 2. During the 24 h following ACTH infusion the concentration of sodium and potassium in plasma and urine showed no significant variation either in treated or in control calves. 3. ACTH infusion induced a significant increase in plasma cortisol levels, which did not appear in control calves. Plasma aldosterone levels did not vary significantly in treated or in control calves.

Adrenal Cortex Hormones↗

PubMed1979

DNA-dependent ATPases from Escherichia coli K12.

Four DNA-dependent ATPases have been isolated from E. coli extracts. ATPases I and III, both sensitive to NEM, require denatured DNA but differ in their heat sensitivity, elution from DEAE-cellulose, and sedimentation coefficient. ATPases II and IV are both resistant to NEM. ATPase II requires partially denatured DNA, whereas ATPase IV can be stimulated by SS DNA. ATPase I is a DNA-unwinding enzyme; ATPase II may be involved in recombination.

Adenosine Triphosphatases↗

PubMed1978

Purification and characterization of DNA-dependent ATPase II from Escherichia coli.

A new DNA-dependent ATPase was isolated and purified from soluble extracts of Escherichia coli. This enzyme, called ATPase II, has a molecular weight of 86,000 and exists in a monomeric state. It degrades ATP (or dATP) to ADP (or dADP) and Pi in the presence of magnesium and requires a double-stranded polynucleotide as cofactor. A correlation between the efficiency as cofactor and the melting point of the polynucleotide has been found; the lower the melting temperature, the higher the stimulation of ATPase II. The enzyme binds to single-stranded DNA and poly[d(A-T)] copolymer, but not to the double-stranded circular DNA (Form I) of simian virus 40.

Adenosine Triphosphatases↗

PubMed1976

Purification and characterization of a DNA-dependent ATPase from Escherichia coli.

A DNA-dependent ATPase has been isolated and purified from an Escherichia coli cell-free extract. The ATPase has the following characteristics: preferential dependence on single-stranded DNA, specificity for ATP hydrolysis, Km value of 1.4 X 10-4 M for ATP, and molecular weight of approximately 69,000. The ATPase can be shown to bind to single stranded DNA. The resemblance between this ATPase and that isolated from vaccinia cores is discussed.

Adenosine Triphosphatases↗