scholarly journals Characterization of the vitamin D-dependent Ca2+-binding sites in rat intestinal Golgi-enriched membrane fractions

1984 ◽  
Vol 218 (2) ◽  
pp. 347-354 ◽  
Author(s):  
J R F Walters ◽  
M M Weiser
Keyword(s):  
Vitamin D ◽  
Ionic Strength ◽  
Vitamin D Deficiency ◽  
Binding Sites ◽  
Control Diet ◽  
Specific Protein ◽  
High Affinity ◽  
Equilibrium Binding ◽  
Number Of Binding Sites

Rat intestinal Golgi-enriched membrane fractions take up Ca2+ by a vitamin D-dependent process that has been shown to recover within 15 min of repletion of vitamin D-deficient animals with intravenous 1,25-dihydroxycholecalciferol. The present paper reports studies characterizing the Ca2+-binding sites of these membrane fractions. Equilibrium binding of Ca2+ at concentrations between 5 and 400 microM showed significant decreases at all concentrations in membranes derived from vitamin D-deficient animals when compared with normal control-diet-fed animals. The predominant class of binding sites had a relatively high affinity for Ca2+ (KD approx. 3 microM). Vitamin D-deficiency did not change the affinity of this class of site, but decreased the number from 347 +/- 26 to 168 +/- 50 nmol of Ca2+ bound/mg of protein (means +/- S.D.). Mg2+ inhibited binding only at low Ca2+ concentrations, and the characteristics of this binding suggested positive co-operativity between two binding sites. Equimolar concentrations of Zn2+, La3+, Pb2+ and Mn2+ inhibited Ca2+ binding by over 50%. Increased ionic strength decreased Ca2+ binding by no more than half. Binding was maximal at pH 7.5 and half-maximal at pH 6.3. The large number of binding sites with relatively high affinity for Ca2+ suggests that it is unlikely that this binding is to any specific protein or to non-specific sites present on many proteins, and that the most likely sites are lipid molecules.

Characterization of Thromboxane A2/Prostaglandin H2 Receptors in Porcine Coronary Artery -The Inhibitory Effect of a Novel Dibenzoxepin Derivative, KW-3635

1992 ◽  
Vol 67 (05) ◽  
pp. 582-584 ◽  
Author(s):  
Ichiro Miki ◽  
Akio Ishii
Keyword(s):  
Coronary Artery ◽  
Binding Sites ◽  
Thromboxane A2 ◽  
Inhibitory Effect ◽  
Scatchard Analysis ◽  
Single Class ◽  
Porcine Coronary Artery ◽  
Equilibrium Binding ◽  
H2 Receptors

SummaryWe characterized the thromboxane A2/prostaglandin H2 receptors in porcine coronary artery. The binding of [3H]SQ 29,548, a thromboxane A2 antagonist, to coronary arterial membranes was saturable and displaceable. Scatchard analysis of equilibrium binding showed a single class of high affinity binding sites with a dissociation constant of 18.5 ±1.0 nM and the maximum binding of 80.7 ± 5.2 fmol/mg protein. [3H]SQ 29,548 binding was concentration-dependently inhibited by thromboxane A2 antagonists such as SQ 29,548, BM13505 and BM13177 or the thromboxane A2 agonists such as U46619 and U44069. KW-3635, a novel dibenzoxepin derivative, concentration-dependently inhibited the [3H]SQ 29,548 binding to thromboxane A2/prosta-glandin H2 receptors in coronary artery with an inhibition constant of 6.0 ± 0.69 nM (mean ± S.E.M.).

The Temporal Distribution of the 1α,25-Dihydroxycholecalciferol Receptor in the Rat Jejunal Villus

1984 ◽  
Vol 67 (3) ◽  
pp. 285-290 ◽  
Author(s):  
S. D. H. Chan ◽  
D. Atkins
Keyword(s):  
Vitamin D ◽  
Vitamin D Deficiency ◽  
Calcium Absorption ◽  
Sedimentation Coefficient ◽  
Temporal Distribution ◽  
High Affinity ◽  
High Affinity Receptor ◽  
Affinity Receptor ◽  
Cell Fractions ◽  
Crypt Cells

1. The distribution of the 1α,25-dihydroxycholecalciferol receptor was studied in enterocytes isolated from the upper, mid and lower villus and crypt cells of the jejunum of normal and rachitic rats. 2. In all cell fractions a high-affinity receptor (KD ⋍ 0.07 nmol/l) with a sedimentation coefficient of 3.5S was demonstrated. 3. In normal rats there was a 60% reduction in receptor numbers in crypt cells compared with the mid and upper villous cells. 4. Vitamin D deficiency led to a reduction in receptor numbers in all cell fractions (45% upper villus, 78% crypt cells). 5. The data are compatible with the concept of calcium absorption occurring in the differentiated villous cells and also account for the reduction in absorption in rachitic animals.

Phosphorus adaptation in rats in absence of vitamin D or parathyroid glands

1980 ◽  
Vol 239 (4) ◽  
pp. G261-G265
Author(s):  
C. F. Cramer ◽  
J. McMillan
Keyword(s):  
Vitamin D ◽  
Urinary Excretion ◽  
Vitamin D Deficiency ◽  
Intestinal Absorption ◽  
Control Diet ◽  
Inorganic Phosphorus ◽  
Parathyroid Glands ◽  
Intestinal Excretion ◽  
Growing Rats ◽  
Pi Deficiency

Growing rats even when vitamin D deficient became adapted to inorganic phosphorus (Pi) deficiency by increasing absorption and minimizing excretion. Feeding low-Pi diet for 3 wk reduced urinary Pi by 80% (P < 0.001), and urinary 32P by 50% (P < 0.001). Low-Pi regimen increased 32p absorption from a 32P-labeled meal by 50% (P < 0.001), even when the animals were vitamin D deficient or thyroparathyroidectomized. The marked increase in retention of 32P in phosphorus-deficient rats could not be accounted for by decreased endogenous intestinal excretion plus increased kidney reabsorption; increased intestinal absorption played a part. 32P absorption was significantly reduced (P < 0.001) by vitamin D deficiency in rats fed either control diet (.6%) Pi or low-Pi diet (0.03%). Endogenous intestinal or urinary excretion of 32P was unaltered by vitamin D deficiency. The evidence supports the hypothesis that there are two mechanisms for phosphorus adaptation: kidney retention not requiring vitamin D, and inreased intestinal absorption of Pi not requiring parathyroids, thyroids, or vitamin D.

scholarly journals The binding of spermine to the ribosomes and ribosomal ribonucleic acid from Bacillus stearothermophilus

1969 ◽  
Vol 113 (1) ◽  
pp. 117-121 ◽  
Author(s):  
L. Stevens
Keyword(s):  
Ionic Strength ◽  
Ribosomal Rna ◽  
Ribonucleic Acid ◽  
Binding Sites ◽  
Bacillus Stearothermophilus ◽  
Gel Filtration ◽  
Ribosomal Ribonucleic Acid ◽  
Number Of Binding Sites ◽  
Filtration Technique

1. The total intracellular concentrations of Na+, K+, Mg2+, spermine, spermidine and RNA were measured in Bacillus stearothermophilus. 2. The binding of spermine to ribosomes and to ribosomal RNA from B. stearothermophilus was studied under various conditions by using a gel-filtration technique. 3. The affinity of spermine for ribosomes and for ribosomal RNA decreased with increasing ionic strength of the medium in which they were suspended. 4. The extent of spermine binding did not change appreciably in the temperature range 4–60°. 5. Optimum binding occurred at about pH7·0. 6. The number of binding sites for spermine on either ribosomes or ribosomal RNA was 0·10–0·13/RNA phosphate group. 7. A high proportion of the intracellular spermine is likely to be bound to the ribosomes in vivo; spermine competes with Mg2+ on equal terms for sites on the ribosomes.

scholarly journals Inhibition of the soluble adenosine triphosphatase from mitochondria by adenylyl imidodiphosphate

1974 ◽  
Vol 143 (3) ◽  
pp. 745-749 ◽  
Author(s):  
Roger D. Philo ◽  
Michael J. Selwyn
Keyword(s):  
Atpase Activity ◽  
Rate Constants ◽  
Binding Sites ◽  
Adenosine Triphosphatase ◽  
Reaction Rate ◽  
Dissociation Reaction ◽  
Reaction Rate Constants ◽  
High Affinity ◽  
Number Of Binding Sites ◽  
Inosine Triphosphatase

1. Adenylyl imidodiphosphate is an inhibitor with high affinity for the soluble ATPase (adenosine triphosphatase) from mitochondria. 2. The reaction of the inhibitor with the ATPase is slow and estimates for the association and dissociation reaction rate constants are given. 3. The number of binding sites for the inhibitor appears to be doubled in the presence of 2,4-dinitrophenol. 4. Adenylyl imidodiphosphate is less effective as an inhibitor of the ATPase activity of this enzyme than of the inosine triphosphatase activity. It is also less effective on the ATPase of frozen-thawed or intact mitochondria and did not inhibit ADP-stimulated respiration by intact mitochondria.

Sign in / Sign up

Export Citation Format

Share Document