Progesterone receptor in the chick thymus

Specific, high affinity binding sites for progesterone and promegestone /R-5020/ have been shown to be present in the chick thymus measured by experiments with intact cells or under cell-free conditions. In isolated thymocytes most of the receptor-R-5020 complex is bound to the nucleus. Dissociation constants were determined in thymic cytosol by Scatchard plot analysis and were found to be 3.1 and 2.6 nM for progesterone and R-5020, respectively. On the basis of competition assays the binding sites seemed to be specific for progesterone and R-5020. Glucocorticoids bind only slightly and only at high concentrations. By gel-filtration experiments the thymic R-5020 binding site was shown to be a macromolecule. In vivo treatment of chicks with progesterone or R-5020 caused a significant increase in thymidine kinase activity of the thymus.     

Isolation of riboflavin carrier proteins from pregnant human and umbilical cord serum: Similarities with chicken egg riboflavin carrier protein

A riboflavin carrier protein has been purified from human pregnancy and umbilical cord sera by affinity chromatography and fast protein liquid chromatography. This protein has a similar molecular weight to the chicken egg riboflavin carrier protein and shares other physicochemical properties, such as pI and riboflavin binding characteristics, with the avian counterpart. A high degree of immunological cross-reactivity is observed between the human and avian riboflavin binding proteins indicating the extensive conservation of this protein throughout evolution.     

Photosynthetic activity of diimidoester-modified cells,permeaplasts, and cell-free membrane fragments of the blue-green alga Anacystis nidulans

On treating the blue-green alga Anacystis nidulans with dimethylsuberimidate up to 70% of the free NH₂ of the photosynthetic membrane is amidinated, and presumably inter- and intramolecular cross-links are established in the membrane proteins. Amidination destroys the ability of A. nidulans to photoreduce HCO₃^? but leaves the photochemical activities of Photosystems II and I nearly intact. With added electron acceptors, photosynthetic O₂ evolution can be demonstrated both with permeable cells (permeaplasts) prepared by digestion of the cell wall of dimethylsuberimidate-reacted A. nidulans with lysozyme, as well as with heavy membrane particles (36 000 × g) prepared from dimethylsuberimidate-reacted cells.Permeaplasts prepared from dimethylsuberimidate-reacted cells resist damage in hypoosmotic medium, whereas those prepared from unreacted cells are induced to release C-phycocyanin. On the other hand, the former are inactivated more easily by heat stress than the latter. On this basis, it is concluded that cross-linking with dimethylsuberimidate confers functional instability to photosynthetic membranes.