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Biomedical subjects

S Formisano

Publications and source records attributed to S Formisano.

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

Critical micelle concentrations of gangliosides.

The micellar properties of mixed, bovine gangliosides and purified galactosyl-N-acetylacetylgalactosaminyl (N-acetylneuraminyl) galactosylglucosylceramide were studied by gel filtration, equilibrium dialysis, and band and boundary centrifugation in sucrose gradients. The dissociation of micelles is very slow (days) in water and required us to approach equilibrium by association of monomers rather than by the dissociation of micelles. The gangliosides were therefore first converted into very low molecular weight aggregates (1-3 molecules) by dissolving them in Me2SO. Galactosyl-N-acetylgalactosaminyl(N-acetylneuraminyl)galactosylglucosylceramide was then diluted into aqueous sucrose gradients and sedimented by the boundary centrifugation technique. This gave a sedimenting micelle and a nonsedimenting monomer concentration of (1-2) x 10-10 M (or less) which corresponds to the critical micelle concentration value. The mixed gangliosides revealed two micellar sizes (i.e., 10 and 4.5 S), the slower sedimenting species being formed from the larger one with time (days). The critical micelle concentration of the mixed gangliosides was found to be approximately 10-8 M by a gel filtration, equilibrium dialysis, and band centrifugation.

Animals↗
PubMed1978

Effects of Hofmeister salts on the self-association of glucagon.

The trimerization constants of glucagon at pH 10.6 in 0.76 M K2HPO4 have been calculated from circular dichroism data between 5 and 50 degrees C. The free energy, enthalpy, and entropy of transfer have been evaluated from the current results and published data in 0.20 M phosphate. The free energies of transfer are derived completely from an increase in the entropy of transfer, since the enthalpy of transfer is less favorable at all temperatures. These parameters are compared with those of various model groups and compounds: CH2, peptide, methane, ethane, and the 1--13 N-terminal fragments of ribonuclease. The effects of fluoride and chloride on the self-association of glucagon have been compared with that of phosphate at 25 degrees C. These effects are consistent with the binding of approximately one molecule of salt to the trimer and a systematic decrease in the number of water molecules bound to the trimer compared to the monomer for the series K2HPO4, KF, and KCl.

Anions↗
PubMed1978

Self-association of glucagon as measured by the optical properties of rhodamine 6G.

The fluorescence of rhodamine 6G is completely quenched in glucagon solutions in 0.6 M K2HOP4 at pH 10.6. The absorption of rhodamine 6G is red-shifted by the same reaction. A single rhodamine 6G molecule appears to be bound to a hydrophobic patch in the center of the trimer of glucagon. Since the glucagon monomer has almost no organized structure this site exists only in the associated trimer form of glucagon. The self-association of glucagon to the trimer has been determined from the variation in rhodamine 6G fluorescence and absorption measured over a 60-fold range of dye concentration. The self-association constant agrees with values determined by other methods in the absence of dye. The binding isotherms of rhodamine 6G to glucagon shift with glucagon concentration and exhibit negative cooperativity.

Anilino Naphthalenesulfonates↗
PubMed1978

Effect of pressure and ionic strength on the self-association of Apo-A-I from the human high density lipoprotein complex.

The self-association of apo-A-I isolated from the human high density lipoprotein complex has been investigated by gel permeation chromatography and sedimentation equilibrium. The apparent weight average molecular weight (MWapp) versus Apo-A-I concentration profile was found to be sensitive to ionic strength and pressure; MWapp increased with increasing ionic strength and decreasing rotor speed. The data were consistent with a monomer-dimer-tetrameroctamer association shceme over all conditions investigated if a change in the partial specific volume of apo-A-I upon association of 5.5 x 10(-2) ml/g is postulated.

Apolipoproteins↗
PubMed1977

Thermodynamics of the self-association of glucagon.

In water, glucagon exists in an equilibrium between a trimer in which more than half of the peptide groups are in an alpha-helical configuration and a monomer which has a random coil configuration with few alpha-helical residues. The thermodynamics of this self-association have been evaluated by studying the temperature- and concentration-dependence of the mean residue ellipticity at 220 nm. The enthalpy and entropy changes of association were negative at all temperatures between 5 degrees and 50 degrees and had large negative temperature dependencies. Usually an association that involves nonpolar groups is considered to be driven by a positive entropy term. Such an explanation is not tenable in the case of glucagon. However, if the effects of nonpolar groups on the coil-to-helix transition of a polypeptide are included into the thermodynamic considerations of hydrophobic interactions, then the negative parameters observed for glucagon association can be readily understood. The hydrophobic interaction is therefore not necessarily controlled by the entropy change because, if there are significant conformational changes, the reaction may be controlled by the enthalpy change. Consequently, the more important parameter characteristic of all hydrophobic reactions is the heat capacity change.

Glucagon↗
PubMed1975

[Iodoamino acid composition of rat thyroglobulin of varying total iodine concentration and fractions isolated by isopycnic ultracentrifugation].

Iodoaminoacid content (iodothyronines, T3 and T4, and iodotyrosines, MIT and DIT) has been determined in enzymatic hydrolysates of thyroglobulin Tg 19S of different iodine content (0.3-0.9%) isolated from equilibrium labeled rats. Preparative equilibrium centrifugation in RbCl density gradients of pure thyroglobulin was used to obtain protein fractions of largely different iodine content (0.2-1.2% I). Thin layer chromatography of total hydrolysates demonstrated that the distribution of iodoaminoacids depends on the total iodine content of each fraction. It is concluded, in agreement with previous results, that the native structure of Tg is an important factor in the regulation of hormone biosynthesis and that even at low iodination levels of Tg. T3 and T4 are synthesized.

Amino Acids↗
PubMedDate not supplied

Functional and biochemical evidence of a specific adenosine A2/Ra receptor on human platelets.

5'-N-ethylcarboxamideadenosine (NECA) greater than 2-chloroadenosine greater than adenosine greater than (-)-N6-(R-phenyl-isopropyl)-adenosine [(-)-R-PIA] greater than (+)-N6-(S-phenyl-isopropyl)-adenosine [(+)-S-PIA] inhibited in vitro human platelet aggregation in a dose-dependent fashion. 6-nitrobenzylthioinosine and dipyridamole, which inhibit adenosine uptake, and erythro-9-(2-hydroxy-3-nonyl)-adenine, which blocks adenosine metabolism, did not impair the inhibition induced by NECA and adenosine. 8-phenyltheophylline and theophylline, two competitive antagonists of adenosine receptors, blocked the inhibition of platelet aggregation caused by NECA and adenosine. NECA greater than 2-chloroadenosine greater than adenosine greater than (-)-R-PIA greater than (+)-S-PIA increased platelet cyclic adenosine monophosphate (cAMP) levels in a dose-dependent fashion. A significant linear correlation (r = 0.70, p less than 0.001) was found between the increase of platelet cAMP and the inhibition of platelet aggregation induced by adenosine and its analogs. 8-phenyltheophylline, which is a competitive antagonist of adenosine in platelets, also blocked the cAMP accumulation caused by NECA. These data suggest that NECA and other adenosine analogs activate a specific cell surface adenylate cyclase-linked adenosine receptor whose properties are similar to those of an adenosine A2/Ra receptor.

Adenosine↗