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Y Combarnous

Publications and source records attributed to Y Combarnous.

52 records · Page 3Linked to original sources
PubMed1981

Physico-chemical properties of pregnant mare serum gonadotropin.

Pregnant mare serum gonadotropin exhibits a dissociation at acid pH as shown by the drop of s20,w values from 3.52 S at pH 8.1 to 2.52 S at pH 2.0. The dissociation is accompanied by an absorbance change with a maximum at 287 nm and a parallel loss of both follicle-stimulating hormone (FSH) and luteinizing hormone (LH) activities as followed by radioreceptor assays. The apparent pKa of the acid transition is 3.45 with an extremely slow and temperature-dependent rate at pH 2.0 (1.8 . 10(-4) s-1 at 37 degrees C). By gel filtration the molecular weight of the active hormone is estimated to be 45 000 (rather than the previously reported 53 000-64 000). The active conformation of the hormone includes beta sheet structure (34%) as for other gonadotropin hormones with a minor but significative amount of alpha-helix. Four tyrosine residues were titrated, two of pKa = 10.3 and two of pKa = 11 out of a total of seven tyrosines. The parallel changes in FSH and LH activities during the preparation and the acid transition suggest that the two biological activities are intrinsic properties of the same molecular entity.

Animals↗
PubMed1978

Study of follitropin receptors in testis using a homologous system. Binding of porcine follitropin to plasma membranes from immature porcine testis and correlation with adenylate cyclase stimulation.

The properties of follitropin receptors in immature porcine testis were determined using highly purified porcine follitropin. 1. The characteristics of follitropin binding to a subcellular fraction rich in plasma membranes were studied using a 125I-labelled follitropin with high specific activity (75-100 Ci/g) and high binding activity. The binding is dependent on time, temperature and pH. It is specific to follitropin as demonstrated by the very low binding activity of the follitropin alpha and beta subunits and of the other glycoprotein hormones. Scatchard analysis of binding data indicated an equilibrium association constant of 2 x 10(10) M-1 and a concentration of high affinity binding sites of 500 fmol/mg membrane proteins. 2. A sensitive radio-ligand receptor assay was developed. Fifty percent inhibition of binding was obtained with as little as 2 ng of porcine follitropin. Ovine and bovine follitropins and pregnant mare serum gonadotropin gave binding inhibition curves parallel to that given by porcine follitropin. With equine and human follitropin, significantly different slopes were recorded. 3. Kinetics of dissociation of labelled follitropin from its testis receptors showed the presence of at least two compartments with fast and slow dissociation rate constants. The ratio between the sizes of the slow and fast compartments appeared dependent upon preincubation time. 4. A temporal correlation was observed between binding of follitropin to testis receptors and activation of membrane bound adenylate cyclase.

Adenylyl Cyclases↗
PubMed1976

Chemical study of the topography of porcine lutropin (LH) using dinitrofluorobenzene and dansyl chloride.

Treatment of porcine lutropin beta-subunit by increasing amounts of dansyl chloride shows that only one fluorescent group can be bound to the free subunit, namely on tyrosine beta-37. This modification prevents reassociation with native chi-subunit. In contrast to dansyl chloride, dinitrofluorobenzene reacts preferentially with tyrosine beta-59. This substitution does not interfere with the reassociation with the native chi-subunit. By using equimolar ratio of dansyl chloride and porcine lutropin chi-subunit it is possible to modify this subunit on a single site, which is found to be a tyrosine residue. The monodansylated X-subunit is still able to recombine with native B-subunit but its fluorescence is found to be markedly quenched upon binding. In addition, the O-dansyl-tyrosyl fluorescence quenching by potassium iodide is more effective on the recombined dimer than on the free chi-subunit. Both reconstituted dimers (native xhi chi dinitrophenylated beta and dansylated chi chi native beta) are without biological activity. It is not clear whether the substituted phenolic groups are essential or whether the added groups prevent the chi beta dimer from taking the active conformation. This alternative is discussed in the light of recent data from this laboratory and others.

Amino Acids↗
PubMedDate not supplied

Purification and characterization of luteinizing hormone from the dromedary (Camelus dromedarius).

Luteinizing hormone (LH) has been purified from 150 dromedary pituitaries and its partial physicochemical, biological and immunological characterization has been achieved. Purification of the hormone was monitored by a porcine LH radioreceptor assay (RRA). In this system, the final camLH preparation exhibited an activity 0.6-fold that of highly purified porcine LH. The acid half-dissociation of camLH at equilibrium was observed at pH 4.2. A homologous camLH RRA was developed using the testicular plasma membrane fraction from prepubertal camels and radioiodinated, highly-purified camLH. Pituitary and chorionic gonadotropins (CG) from several mammalian species were compared to camLH in this system. The equine gonadotropins eLH and eCG were shown to be 6 times less potent in the camel RRA than in the porcine RRA, whereas the LH from other species exhibited similar activities in both systems. This particularity of camel LH receptors offers a new tool for the study of structural features of gonatropin interactions with their receptors.

Animals↗