High Affinity Binding Capacity Research Articles

25-Hydroxycholecalciferol-binding protein: Partial purification from rat duodenal mucosa cells

The 25-hydroxycholecalciferol-binding protein has been partially purified (purification factor: 37) from rat duodenal cytosol, using chromatographic procedures on gel and ionic exchange resin. This partially purified protein bound 25-hydroxycholecalciferol with high affinity (K D = 5.7 × 10 −9M) and low binding capacity (23 × 10 −12 mole/mg of protein. Using a rabbit antiserum obtained against such partially purified protein, we demonstrated that 25-hydroxycholecalciferol cytosolic binder and 25-hydroxycholecalciferol plasmatic binding share common antigenic sites.

Binding of [ 3H]guanylylimidodiphosphate to membranes: Lack of correlation with adenylate cyclase activation

The binding of tritiated guanylylimidodiphosphate ([ 3H]GMP-P(NH)P) to turkey erythrocyte ghosts was studied in parallel with the activation by GMP-P(NH)P of adenylate cyclase. The high affinity binding capacity for GMP-P(NH)P, 50 pmoles per mg protein, exceeds the estimated quantity of adenylate cyclase of 1 pmole per mg of protein. The rate of nucleotide binding is not affected by isoproterenol. Further, in the presence of the hormone the rate of binding is much slower than the rate of activation. Although the rate of dissociation of bound [ 3H]GMP-P(NH)P is negligible at 37°, it is increased dramatically by unlabeled GMP-P(NH)P, GTP, EDTA, ATP, AMP-P(CH 2)P, or p-aminophenylmercuric acetate. In contrast, the rate of decay of the GMP-P(NH)P-simulated state is not altered by these agents. Thus, the major fraction of GMP-P(NH)P binding to membranes is not relevant to cyclase activation.

Récepteurs de l'oestradiol-17β dans le foie de poule et de l'amphibien Discoglossus pictus

Estradiol -17β receptors in the liver of chicken and the amphibian Discoglossus pictus The evidence of an estrophilic macromolecule in chicken liver anf amphibian liver ( Discoglossus pictus ) has been demonstrated. In both species a receptor of high affinity ( K D ≈ 3 · 10 −10 M) and low binding capacity (0.7 · 10 −15 mole of estradiol/ mg tissue in chicken liver and 0.2 · 10 −15 mole of estradiol/mg tissue in Discoglossus liver) is present in the nuclear fraction; it binds estrogens (estradiol, estrone and estriol) but not non-estrogenic hormones. No receptor occurs in the cytosol fraction. The sedimentation analysis (sucrose density gradient 5–20%) of nuclear extract from Discoglossus liver (animals implanted with pellets of 500 μg estradiol) shows a peak approx. 4 S, sensitive to proteolytic enzymes.

A soluble, heat-labile, high-affinity Ca 2+-binding factor extracted from rat liver mitochondria

Rat liver mitochondria exposed to osmotic shock (distilled water) lose the capacity for high-affinity binding of Ca 2+. The Ca 2+ binding activity can be recovered in soluble form in the extract. It is heat-labile, not affected by uncouplers or respiratory inhibitors, and is inhibited by Sr 2+, Mn 2+, La 3+, but not by Mg 2+. The particle weight of the soluble factor exceeds 150,000.