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Biomedical subjects

P Marche

Publications and source records attributed to P Marche.

84 records · Page 5Linked to original sources
PubMed1978

Intestinal calcium-binding protein (CaBP) and bone calcium mobilization in response to 25R,26 and 25S,26-dihydroxycholecalciferol in intact and nephrectomized rats.

Since intestinal calcium-binding protein (CaBP) can be regarded as an expression of the hormone-like action of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on the duodenal enterocyte we have investigated the potential biological activity of 25R and 25S,26-(OH)2D3 (two recently synthesized epimers of vitamin D3 metabolite) to promote intestinal CaBP production as compared to bone calcium mobilization in vitamin D and calcium-deficient rats. In our assay steroids exhibited a 72 hour calcemic response. Our results show a linear relationship between CaBP synthesis and the logarithm of the dose (130-2080 pmol dose range) of either 25R or 25S epimer. The CaBP response was comparable for both epimers. Similarly bone calcium mobilization response was dose related as a linear function of the logarithm of the administered dose. Again, calcemic response was comparable for both epimers. In our model these two epimers were about as active on intestine to increase CaBP amount as on bone to elevate serum calcium level. Bilateral nephrectomy abolished CaBP response to a large dose (1040 pmol) of either 25R or 25S epimer but did not abolish it to a 130 pmol dose of 1alpha,25-(OH)2D3.

Animals↗
PubMed1976

Conformational characteristics of luliberin. Circular dichroism and fluorescence studies.

By circular dichroism and fluorescence spectroscopy, the conformation of luliberin (luteinizing hormone-releasing hormone) has been investigated under various conditions of pH and solvents. Several structural parameters have been defined which seem predominant for the maintenance of the hormone in some privileged conformation(s). Formation of an intramolecular hydrogen bond between CO (His) and NH (Ser) seems likely when dissolving the hormone in organic solvent such as dioxane. Energy transfer has been demonstrated between Tyr and Trp residues. Calculation of the energy-transfer efficiency at different pH's allowed us to estimate in the range of 10 A the distance which separates these residues. Evidence is also provided for a charge-transfer interaction between protonated histidine and tryptophan. These data suggest that, when luliberin has organized structure (under appropriate surrounding conditions), its conformational pattern would resemble that of beta-turn structure in which a beta bend would exist at the level of the aromatic residues.

Circular Dichroism↗
PubMed1976

Conformational characteristics of luliberin. Luminescence properties at liquid-nitrogen temperature.

The luminescence properties (fluorescence and phosphorescence) of luliberin have been investigated at liquid-nitrogen temperature (77 K) in 50% ethylene glycolaqueous buffer at various pH's. Calculation of the energy-transfer efficiency between Trp and Tyr residues leads to an evaluation of the distance separating these residues. In alkaline medium, when tyrosine is ionized, a 100% transfer efficiency occurs from Trp to Tyr- at the singlet level and also from Tyr- to Trp at the triplet level indicating that the TRP-Tyr distance is less than about 5A. When luliberin is at pH 7.8 (or 4.5), transfer efficiency from Tyr to Trp at the singlet level is 85-90% which should correspond to a distance between Trp and Tyr of about 10-12 A. These results are discussed with respect to the role played by aromatic amino acids both in the hormone conformation and in the hormone biological potency. Moreover, comparison with the data obtained from fluorescence or circular dichroism studies at room temperature allows us to deduce some characteristics of luliberin conformation. Structure-activity relationships in the aromatic region of luliberin are also discussed.

Circular Dichroism↗
PubMed1975

Specific tritiation of indole derivatives by catalytic desulfenylation. Application to the labelling of tryptophan-containing peptides.

A new method for tritiating indole derivatives was studied. The procedure consisted first of the formation of an o-nitrophenylsulfenyl tryptophanyl derivative by reacting the compound with o-nitrophenylsulfenyl chloride; then the sulfenylated product was submitted to catalytic hydrogenolysis in the presence of tritium gas. This latter reaction led to the desulfenylation of the compound and permitted the replacement of the thioether function by a tritium atom. By this procedure l-tryptophan, N-acetyl-l-tryptophanamide and a gastin-like pentapeptide derivative, Boc-Gly-Trp-Met-Asp-Phe(NH2), have been tritiated; 15, 16 and 7 Ci/mmol have been obtained respectively. The labelled compounds have retained the properties of the native materials.

Animals↗
PubMedDate not supplied

Altered turnover of polyphosphoinositides in the erythrocyte membrane of the spontaneously hypertensive rat.

The metabolism of inositol phospholipids of the erythrocyte membrane was compared in normotensive Wistar-Kyoto (WKY), spontaneously hypertensive (SHR), and stroke-prone SHR (SHR-SP) rats. This was performed on isolated ghost membranes by measuring the incorporation of 32P from [ gamma-32P ] adenosine triphosphate (ATP) into the diphosphoinositides (DPI) and the triphosphoinositides (TPI) which were the only 32P-labeled phospholipids. 32P-labeling of TPI was altered in adult and 3-week-old SHR as well as in SHR-SP compared to WKY controls; the radioactivity associated with TPI in hypertensive rats was about 30% lower than that associated with TPI in age-matched normotensive controls. By contrast, the radioactivity associated with DPI was similar in both hypertensive and normotensive rats. Measurement of the phosphoinositide distribution in both SHR and WKY indicates that the change observed in 32P-TPI could not be accounted for by a reduced phosphatidylinositol content in SHR membrane. Measurement of the Mg2+-activated TPI-phosphomonoesterase and of the Ca2+-activated polyphosphoinositide phosphodiesterase activities did not show any significant difference between SHR and WKY. It thus appears that the altered phosphoinositide metabolism observed in hypertensive rats was a consequence of some alteration in the activity of kinases which are responsible for the conversion of phosphatidylinositol into DPI and TPI. These results also suggest that the defect in phosphoinositide metabolism observed in genetically hypertensive rats was not a consequence of the blood pressure elevation and could be related to the pathogenesis of hypertension.

Animals↗