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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The composition of skeletal muscle microsomes is reviewed. Evidence for the involvement of cholesterol in the transport of calcium by vesicles derived from the sarcoplasmic reticulum is considered. Results obtained by non aqueous extractions of skeletal muscle microsomes, and by use of the cholesterol analogue 20, 25 diazacholesterol indicate that cholesterol is not involved in calcium transport by vesicles of sarcoplasmic reticulum origin. Use of density perturbation procedures indicating that cholesterol is present in muscle membranes other than those of the sarcoplasmic reticulum involved in calcium transport is discussed. The distribution of membranal cholesterol in muscle is compared to that in other tissues.
Mol Cell Biochem 1977 Oct 07
PMID:Cholesterol in muscle membranes. 14 66

Controlled tryptic digestion of purified rat skeletal muscle sarcoplasmic reticulum (Ca2+ + Mg2+)-adenosine triphosphate yields two products designated Fragments 3a and 3b with molecular weights of 65,000 and 56,000 respectively. The isolation of these products in high yield should facilitate exploration of the molecular characteristics of this adenosine triphosphatase. A simple, rapid method for accomplishing this isolation was developed which provides a high yield and utilizes mild conditions. The fragments obtained by this method were used to determine the phospholipid and sulfhydryl contents of Fragments 3a and 3b. In addition, information was obtained on the orientation of these adenosine triphosphatase components in the enzyme lipoprotein complex.
Mol Cell Biochem 1978 Feb 24
PMID:Isolation of subunits from trypsin-cleaved sarcoplasmic reticulum Ca2+ transport adenosine triphosphatase. 14 1

1. The distribution of ATPase and several marker enzymes was examined after differential and sucrose gradient centrifugation of yeast homogenates. 2. An ATPase activity not sensitive to oligomycin is found exclusively associated with a particulate fraction equilibrating at densities of 1.23-1.25. This particulate material shows the chemical and enzymatic characteristics of the yeast plasma membrane. 3. The pH optimum of the plasma membrane ATPase is 5.6, as compared with 8.5 for the mitochondrial ATPase. In addition to oligomycin, the enzyme is not sensitive to other inhibitors of the mitochondrial ATPase as azide, dicyclohexylcarbodiimide and the mitochondrial ATPase inhibitor protein. It is inhibited by p-chloromercuryphenyl sulfonate, fluoride, quercetin and by the antibiotic Dio-9 but is not affected by ouabain. 4. The plasma membrane ATPase shows a high affinity for ATP (Km = 0.1 mM) and is very specific for this compound, hydrolyzing other nucleotide triphosphates less than 25% as rapidly. No activity was detected with ADP. 5. The enzyme requires a divalent cation for activity and Mg2+ is the most effective. It is not significantly stimulated by K+ or bicarbonate and Ca2+ is inhibitory. 6. The activity cannot be assayed in intact cells unless they are permeabilized with toluene. This suggest that the active site is on the cytoplasmic side of the plasma membrane.
Mol Cell Biochem 1978 Nov 30
PMID:Characterization of the plasma membrane ATPase of Saccharomyces cerevisiae. 15 59

1. 1,25-Dihydroxycholecalciferol (1,25-(OH)2-D3) was given at a dose of 5-0 nmol (2-1 mug) daily by mouth for 4-12 days to three patients with hypophosphataemic (type I), vitamin D-resistant rickets. 2. 1,25-(OH)2-D3 increased intestinal absorption and urinary excretion of calcium without significant effect on the renal handling of phosphate or its plasma concentration. 3. It is concluded that in this type of vitamin D-resistant rickets the renal phosphate abnormality is unlikely to be due to diminished endogenous production of 1,25-(OH)2-D3. 4. The difference between this condition and other hypophosphataemic states is discussed.
Clin Sci Mol Med 1975 Mar
PMID:The effect of 1,25-dihydroxycholecalciferol on renal tubular reabsorption of phosphate, intestinal absorption of calcium and bone histology in hypophosphataemic renal tubular rickets. 16 19

1. The metabolism of an intravenous pulse dose of double-isotope-labelled cholecalciferol has been studied in control subjects with widely differing states of vitamin D nutrition and in patients with primary disorders of parathyroid function. 2. The formation of labelled 1,25-dihydroxy-cholecalciferol [1,25-(OH)2D3] and labelled 24,25-dihydroxycholecalciferol [24,25-(OH)2D3] has been related to the prevailing concentrations in serum of 25-hydroxycholecalciferol [25-(OH)D3], immunoreactive parathyroid hormonel, calcium and orthophosphate (Pi). 3. In control subjects with relative vitamin D deficiency [serum 25-(OH)2D3 was related inversely to the serum 25-(OH)D3 and serum calcium, and directly to serum immunoreactive parathyroid hormone. No formation of 1,25-(OH)2D3 was detectable to form labelled 24,25(OH)2D3 preferentially. 4. No control subject produced significant amounts of both labelled 1,25-(OH)2D3 and labelled 24,25-(OH)2D3 simultaneously. 5. All subjects with primary hyperparathyroidism produced significant amounts of labelled 1,25-(OH)2D3 and labelled 24,25-(OH)2D3 simultaneously; the renal turnover of 25-(OH)D3 was apparently greater than in nutritionally matched controls. Serum labelled 1,25-(OH)2D3 in this disease was not correlated with serum 25-(OH)D3, immunoreactive parathyroid hormone, calcium or Pi. Production of labelled 24,25-(OH)2D3 was inappropriately high for the prevailing nutritional state. 6. The indirectly estimated their concentration of 1,25-(OH)2D3 showed only a fourfold variation in control subjects (45-180 pmol/l), compatible with its having a regulated hormonal function. 7. The data suggest that the production of 1,25-(OH)2D3 from a pulse dose of cholecalciferol is normally regulated, directly or indirectly, by the parathyroid hormone.
Clin Sci Mol Med 1975 May
PMID:Vitamin D metabolism and parathyroid function in man. 16 31

Removal of Ca2+ from the incubation medium by addition of 2 mM ethylene glycol bis-(beta-aminoethyl ether)-N, N'tetraacetic acid (EGTA) leads to at least 75% inhibition of the luteinizing hormone-releasing hormone (LH-RH)-induced accululation of adenosine 3'5'-monophoshpate (cyclic AMP) in rat anterior pituitary gland in vitro. This inhibitory effect of EGTA is reversed by the addition of Ca2+. A half-maximal effect of Ca2+ on LH-RH--induced cyclic AMP accumulation is observed at 2-5 X 10-5 M free Ca2+. The LH-RH-induced LH and FSH release is completely dependent upon the presence of Ca2+ in the incubation medium, a half-maximal effect being measured at 1-2 X 10-4 M free Ca2+. The basal release release of LH is increased upon Ca2+ removal.
Mol Cell Endocrinol 1975 Jan
PMID:Calcium requirement for stimulation of cyclic AMP accumulation in anterior pituitary gland by LH-RH. 16 1

Synaptosomes isolated from guinea pig brain cortex were stimulated electrically in a medium containing [32P]-orthophosphate. The electrical stimulation caused increased labelling of phosphatidic acid in a synaptic vesicle fraction prepared by osmotic shock of the incubated synaptosomes. Electrical stimulation also provokes transmitter release from the synaptosomes. Both increased phosphatidate labelling and transmitter release required calcium ions in the medium. The effects are discussed in relation to earlier work with acetylcholine and the possible involvement of membrane phosphatidic acid in transmitter release by exocytosis.
Mol Cell Biochem 1975 Aug 30
PMID:Phosphatidic acid metabolism, calcium ions and transmitter release from electrically stimulated synaptosomes. 17 May 6

In mammalian tissues, two types of regulation of the pyruvate dehydrogenase complex have been described: end product inhibition by acetyl CoA and NADH: and the interconversion of an inactive phosphorylated form and an active nonphosphorylated form by an ATP requiring kinase and a specific phosphatase. This article is largely concerned with the latter type of regulation of the complex in adipose tissue by insulin (and other hormones) and in heart muscle by lipid fuels. Effectors of the two interconverting enzymes include pyruvate and ADP which inhibit the kinase, acetoin which activates the kinase and Ca2+ and Mg2+ which both activate the phosphatase and inhibit the kinase. Evidence is presented that all components of the pyruvate dehydrogenase complex including the phosphatase and kinase are located within the inner mitochondrial membrane. Direct measurements of the matrix concentration of substrates and effectors is not possible by techniques presently available. This is the key problem in the identification of the mechansims involved in the alterations in pyruvate dehydrogenase activity observed in adipose tissue and muscle. A number of indirect approaches have been used and these are reviewed. Most hopeful is the recent finding in this laboratory that in both adipose tissue and heart muscle, differences in activity of pyruvate dehydrogenase in the intact tissue persist during preparation and subsequent incubation of mitochondria.
Mol Cell Biochem 1975 Oct 31
PMID:Regulation of mammalian pyruvate dehydrogenase. 17 57

1. Vitamin D-deficient chicks, maintained on a diet adequate in calcium and treated with ethane-1-hydroxy-1,1-diphosphonate for 2 days before a single oral dose of cholecalciferol (vitamin D3), converted the vitamin into 24,25-dihydroxycholecalciferol instead of into the normal metabolite 1,25-dihydroxycholecalciferol. 2. This inhibition of the renal 1-hydroxylase disappeared on withdrawal of the diphosphonate. 3. Kidneys from chicks given diphosphonate for 12 days converted 25-hydroxycholecalciferol into 24,25-dihydroxycholecalciferol on incubation in vitro. 4. The inhibition of the 1-hydroxylase was markedly accelerated by treating the birds with cholecalciferol. 5. No inhibition of renal 1-hydroxylation was observed in birds maintained on a diet low in calcium. 6. A possible mechanism producing this effect is discussed.
Clin Sci Mol Med 1975 Nov
PMID:The effects of a diphosphonate and dietary calcium on the metabolism of vitamin D3 (cholecalciferol) in the chick. 17 77

1. The urinary excretion of inorganic pyrophosphate (PPi), a known inhibitor of the growth and aggregation of crystals of calcium phosphate and calcium oxalate, increases after ingestion of orthophosphate (Pi). This effect may contribute to the apparent ability of oral phosphate to reduce the formation of urinary stones in man. This paper is a study of the mechanism by which Pi increases PPi excretion, investigated by renal clearance techniques in man and renal arterial infusion in dogs. PPi in plasma was measured by an isotope-dilution method after ion-exchange chromatography. 2. The mean renal clearance of endogenous PPi in ten men was 7-9 +/- 1-7 (SE) ml/min, and the mean ratio of PPi clearance to creatinine clearance was 0-08 +/- 0-02 (SE). The oral ingestion of Pi increased the urinary excretion and renal clearance of PPi about threefold, without significantly changing its concentration in plasma. 3. In dogs, the infusion of Pi into one renal artery caused a greater increase in urinary PPi from the infused than from the non-infused kidney, an effect that could be accentuated by simultaneous intravenous infusion of PPi. In dogs, only 1-3% of an injected or infused dose of PPi appeared intact in the urine, regardless of whether it was infused into the systemic or renal circulation. 4. These results suggest that Pi has a direct affect on the kidney to increase the excretion of PPi. It is possible that Pi either interferes with tubular reabsorption of PPi, perhaps by competing for a common tubular transport mechanism, or that Pi diminishes the intrarenal hydrolysis of PPi.
Clin Sci Mol Med 1976 Nov
PMID:The influence of orthophosphate on the renal handling of inorganic pyrophosphate in man and dog. 18 25


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