Photoaffinity labeling of pituitary gonadotropin releasing hormone receptors during the rat estrous cycle

A bioactive photoaffinity derivative of gonadotropin releasing hormone was used to identify pituitary gonadotropin releasing hormone receptors at various stages of the rat estrous cycle. Sodium dodecyl sulfate polyacrylamide gel electrophoresis resulted in the identification of a single specific component with an apparent molecular weight of 60,000 daltons throughout the estrous cycle. The amount of radioactivity incorporated into the 60K dalton band in diestrus and proestrus female rats increased 2.5-fold to that of metestrus and estrus female rats. These findings provide additional evidence for the identification of pituitary gonadotropin releasing hormone receptors.     

Novel cyclic azo-bridged analogs of gonadotropin-releasing hormone.

Five linear analogs of GnRH containing a p-aminophenylalanine (Pap) residue in their sequence and their six corresponding azo-bridged cyclic derivatives were synthesized. The precyclic peptides were prepared on solid-support, while azo-cyclization was performed in solution by diazotization of the p-aminophenylalanine residue followed by intramolecular coupling of the formed diazo salt with either tyrosine or histidine side chains present in the sequence. All peptides were examined for their binding ability to the GnRH receptor expressed on rat pituitary membranes and for their LH-release activity from dispersed rat pituitary cells. Linear analogs 1 i.e [Pap(5)] GnRH and 3, i.e. [Tyr(3), Pap(5)] GnRH, were found to bind to the GnRH receptors only slightly less avidly than native GnRH. Their cyclization, however, led to a marked reduction in the binding capacity, i.e. from IC(50) of 10(-9) M to the 10(-7) M range, and in biopotency, i.e. LH-release. All other linear and cyclic peptides were found to bind selectively to the GnRH receptor only in the low microM range. Only peptide 1 was found comparable to native GnRH in respect to LH-release activity and thus may potentially be a good agonist of the parent peptide. Peptides 1-4, the most potent GnRH receptor binders, were examined for their conformational properties using CD. Cyclic-azo peptides 2 and 4 were further evaluated by NMR spectroscopy in solution combined with molecular modeling. The structural information obtained explains in part the GnRH-like biological activity observed.     

Water response of the hygrochastic skeletons of the true rose of Jericho (Anastatica hierochuntica L.)

Summary The hygrochastic apparatus in Anastatica hierochuntica was investigated from the standpoint of morphology of the skeleton and fruit and its contribution to the regulation of seed dispersal in accordance with the water conditions.Water absorption by the dry skeletons upon shoot immersion under laboratory conditions is a rapid process requiring only a few minutes. It is followed by a slow opening of the curled branches of the skeleton. Maximal opening is attained by the saturated skeletons in approximately 2h. Absorption of water and subsequent opening occur also when only the main root of the skeleton is immersed in water. The process was duplicated also by intact skeletons irrigated in situ. Skeletons closure in response to evaporation is initially slow, noticable curling of the branches obtained only after 60% of the water is lost from the saturated skeletons. Opening of the skeleton exposes most of the fruits to the force of falling raindrops. The fact that no spontaneous opening of fruits occurred under most laboratory procedures of skeleton immersion suggests that in nature two successive processes occur: the skeletons must first uncurl-hygrochasticly so that raindrops can impinge forcefully on the appendages of the fruit valves and thus cause seed release by ombrohydrochory. Under adequate rainfall, the first fruits to open are those at the outer infructescences; heavier rainfall will release seeds from the upper fruits of the inner infructescences, and later, from fruits at their bases. The force that binds the valves of the fruits to the septa is variable, its strength correlated with different structure of the fruist at different positions on the skeleton. This ensures a rate of seed release commensurate with the rainfall, and secures at least a minimum of water for the first seeds. The heterogeneity of skeleton populations insofar as age of the plants is concerned, further ensures that seed dispersal in a given area will be proportional to the amount of rainfall.     

Properties of laccase in Schinus molle

The properties of laccase isolated from Schinus molle, including its MW, amino acid and carbohydrate composition, are described. The enzyme is distinct from Rhus laccase both in K_m and in carbohydrate composition.