scholarly journals Evidence that inositol 1-phosphate in brain of lithium-treated rats results mainly from phosphatidylinositol metabolism

1987 ◽  
Vol 242 (2) ◽  
pp. 517-524 ◽  
Author(s):  
K E Ackermann ◽  
B G Gish ◽  
M P Honchar ◽  
W R Sherman
Keyword(s):  
Rat Brain ◽  
High Speed ◽  
Inositol Phosphate ◽  
Bovine Brain ◽  
Lower Sensitivity ◽  
Inositol 1 ◽  
Rate Of Hydrolysis ◽  
Tissue Contents ◽  
Hydrolysis Of

In cerebral cortex of rats treated with increasing doses of LiCl, the relative concentrations of Ins(1)P, Ins(4)P and Ins(5)P (when InsP is a myo-inositol phosphate) are approx. 10:1:0.2 at all doses. In rats treated with LiCl followed by increasing doses of pilocarpine a similar relationship occurs. myo-Inositol-1-phosphatase (InsP1ase) from bovine brain hydrolyses Ins(1)P, Ins(4)P and Ins(5)P at comparable rates, and these substrates have similar Km values. The hydrolysis of Ins(4)P is inhibited by Li+ to a greater degree than is hydrolysis of Ins(1)P and Ins(5)P. D-Ins(1,4,5)P3 and D-Ins(1,4)P2 are neither substrates nor inhibitors of InsP1ase. A dialysed high-speed supernatant of rat brain showed a greater rate of hydrolysis of Ins(1)P than of D-Ins(1,4)P2 and a lower sensitivity of the bisphosphate hydrolysis to LiCl, as compared with the monophosphate. That enzyme preparation produced Ins(4)P at a greater rate than Ins(1)P when D-Ins(1,4)P2 was the substrate. The amount of D-Ins(3)P [i.e. L-Ins(1)P, possibly from D-Ins(1,3,4)P3] is only 11% of that of D-Ins(1)P on stimulation with pilocarpine in the presence of Li+. DL-Ins(1,4)P2 was hydrolysed by InsP1ase to the extent of about 50%; both Ins(4)P and Ins(1)P are products, the former being produced more rapidly than the latter; apparently L-Ins(1,4)P2 is a substrate for InsP1ase. Li+, but not Ins(2)P, inhibited the hydrolysis of L-Ins(1,4)P2. The following were neither substrates nor inhibitors of InsP1ase; Ins(1,6)P2, Ins(1,2)P2, Ins(1,2,5,6)P4, Ins(1,2,4,5,6)P5, Ins(1,3,4,5,6)P5 and phytic acid. myo-Inositol 1,2-cyclic phosphate was neither substrate nor inhibitor of InsP1ase. We conclude that the 10-fold greater tissue contents of Ins(1)P relative to Ins(4)P in both stimulated and non-stimulated rat brain in vivo are the consequence of a much larger amount of PtdIns metabolism than polyphosphoinositide metabolism under these conditions.

Studies on the mechanism of acute inhibition of thyroglobulin hydrolysis by iodine

1985 ◽  
Vol 108 (4) ◽  
pp. 511-517 ◽  
Author(s):  
Nandalal Bagchi ◽  
Birdie Shivers ◽  
Thomas R. Brown
Keyword(s):  
Time Course ◽  
Period 2 ◽  
Iodotyrosine Deiodinase ◽  
Rate Of Hydrolysis ◽  
Underlying Mechanisms ◽  
Excess Iodide ◽  
Sites Of Action ◽  
Hydrolysis Of

Abstract. Iodine in excess is known to acutely inhibit thyroidal secretion. In the present study we have characterized the time course of the iodine effect in vitro and investigated the underlying mechanisms. Labelled thyroid glands were cultured in vitro in medium containing mononitrotyrosine, an inhibitor of iodotyrosine deiodinase. The rate of hydrolysis of labelled thyroglobulin was measured as the proportion of labelled iodotyrosines and iodothyronines recovered at the end of culture and was used as an index of thyroidal secretion. Thyrotrophin (TSH) administered in vivo acutely stimulated the rate of thyroglobulin hydrolysis. Addition of Nal to the culture medium acutely inhibited both basal and TSH-stimulated thyroglobulin hydrolysis. The effect of iodide was demonstrable after 2 h, maximal after 6 h and was not reversible upon removal of iodide. Iodide abolished the dibutyryl cAMP induced stimulation of thyroglobulin hydrolysis. Iodide required organic binding of iodine for its effect but new protein or RNA synthesis was not necessary. The inhibitory effects of iodide and lysosomotrophic agents such as NH4C1 and chloroquin on thyroglobulin hydrolysis were additive suggesting different sites of action. Iodide added in vitro altered the distribution of label in prelabelled thyroglobulin in a way that suggested increased coupling in the thyroglobulin molecule. These data indicate that 1) the iodide effect occurs progressively over a 6 h period, 2) continued presence of iodide is not necessary once the inhibition is established, 3) iodide exerts its action primarily at a post cAMP, prelysosomal site and 4) the effect requires organic binding of iodine, but not new RNA or protein synthesis. Our data are consistent with the hypothesis that excess iodide acutely inhibits thyroglobulin hydrolysis by increasing the resistance of thyroglobulin to proteolytic degradation through increased iodination and coupling.

Repeated thyrotrophin stimulation of thyroid secretion: lack of refractoriness in vivo

1985 ◽  
Vol 106 (2) ◽  
pp. 153-157
Author(s):  
N. Bagchi ◽  
T. R. Brown
Keyword(s):  
Adenylate Cyclase ◽  
Thyroid Tissue ◽  
Control Group ◽  
Cyclic Amp Accumulation ◽  
Thyroid Glands ◽  
Rate Of Hydrolysis ◽  
Thyroid Secretion ◽  
Hydrolysis Of

ABSTRACT It has been reported that prior exposure of thyroid tissue to TSH in vitro induces a state of refractoriness to new challenges of the hormone. We have investigated the effect of repeated TSH treatment on thyroid secretion to determine whether such refractoriness exists in vivo. The rate of thyroid secretion was estimated by measuring the rate of hydrolysis of labelled thyroglobulin from mouse thyroid glands in vitro. The thyroid glands were labelled in vivo with 131I and then cultured for 20 h in the presence of mononitrotyrosine, an inhibitor of iodotyrosine deiodinase. The rate of hydrolysis of labelled thyroglobulin was measured as the percentage of radioactivity released as free iodotyrosines and iodothyronines into the gland and the medium at the end of incubation. Thyrotrophin was administered in vivo at hourly intervals for 2–4 injections. The corresponding control group received saline injections every hour except for the last injection when they received TSH. The peak rates of thyroglobulin hydrolysis, measured 2 h following the last injection, were similar in animals receiving two, three or four TSH injections and were not different from those in the control groups. Serum tri-iodothyronine and thyroxine concentrations 2 h after the last injection were higher in the groups receiving multiple TSH injections. Thyroidal cyclic AMP accumulation in response to TSH was markedly depressed in the group receiving multiple injections compared with the group receiving a single injection of TSH in vivo. These data indicate that (1) the stimulatory effect of TSH on thyroidal secretion is not diminished by prior administration of the hormone in vivo, (2) repeated TSH administrations in vivo cause refractoriness of the adenylate cyclase response to TSH and (3) a dichotomy exists between the secretory response and the adenylate cyclase response to repeated administrations of TSH. J. Endocr. (1985) 106, 153–157

Oxytocin and vasopressin stimulate inositol phosphate production in human gestational myometrium and decidua cells

1986 ◽  
Vol 6 (7) ◽  
pp. 613-619 ◽  
Author(s):  
Michael P. Schrey ◽  
Alison M. Read ◽  
Philip J. Steer
Keyword(s):  
Arachidonic Acid ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Diacylglycerol Lipase ◽  
Inositol 1 ◽  
Inositol Phosphate Production ◽  
Acid Accumulation ◽  
Free Arachidonic Acid ◽  
Hydrolysis Of ◽  
Related Increase

The involvement of phosphoinositide hydrolysis in the action of oxytocin and vasopressin on the uterus was investigated in gestational myometrium and decidua cells by measuring the production of inositol phosphates. Both peptides stimulated a dose related increase in all three inositol phosphates in myometrium. This may be related to the control of sarcoplasmic Ca++ levels in the myometrium. Oxytocin and vasopressin also stimulated inositol 1-phosphate (IP) production in decidua cells. The hydrolysis of phosphatidylinositol by decidua homogenates exhibited a precursor-product relationship for diacylglycerol and arachidonic acid accumulation. Hence both peptides may mobilise free arachidonic acid, for prostaglandin biosynthesis, from decidua cell phosphoinositides by the sequential action of phospholipase C and diacylglycerol lipase.

scholarly journals Observations on the action of limit dextrinases on amylopectin-like polysaccharides

1973 ◽  
Vol 133 (2) ◽  
pp. 413-416 ◽  
Author(s):  
G. Dunn ◽  
D. G. Hardie ◽  
D. J. Manners
Keyword(s):  
Rate Of Hydrolysis ◽  
Limit Dextrinase ◽  
Hydrolysis Of

The rate of hydrolysis of amylopectin by three different limit dextrinase preparations is only about 15–23% of that of amylopectin β-limit dextrin under similar conditions. On dilution of the enzymes there was no change in specificity. The factors controlling the specificity of the enzyme and the possible significance in vivo of the results are discussed.

A new succinylcholine-based assay of plasma cholinesterase.

1984 ◽  
Vol 30 (2) ◽  
pp. 192-195 ◽  
Author(s):  
M H Abernethy ◽  
P M George ◽  
V E Melton
Keyword(s):  
Hydrogen Peroxide ◽  
Enzyme Activity ◽  
Plasma Cholinesterase ◽  
Choline Oxidase ◽  
Rate Of Hydrolysis ◽  
The Mean ◽  
Variant Enzyme ◽  
Hydrolysis Of

Abstract We describe a new method for measuring the in vitro rate of hydrolysis of the muscle relaxant succinylcholine. This substrate is hydrolyzed by plasma cholinesterase (EC 3.1.1.8). The resulting choline is determined by measuring the hydrogen peroxide formed on its oxidation by choline oxidase (EC 1.1.3.17). This is done by use of phenol and aminoantipyrine coupled to peroxidase, and yields an intense chromophore, Amax 500 nm. The assay requires 0.1 mL of plasma, and is precise and specific. The CV was 2.7% within run, 7.3% between run. For the usual (U variant) enzyme the Km is 53 mumol/L. Enzyme activity is removed by anticholinesterase antiserum, and is inhibited by dibucaine with a Ki of 2 mumol/L. Ten samples can be assayed in duplicate in an hour. This method is suited to routine use in any laboratory that has a simple spectrophotometer. The mean activity in 11 individuals with the cholinesterase phenotype UU was 105 U/L, for seven UA heterozygotes 61 U/L, and for three AA homozygotes 4 U/L. To the extent allowed by extrapolation from in vitro to in vivo results, this method should increase diagnostic accuracy and may directly predict duration of succinylcholine-induced apnea.

scholarly journals Calcium-activated hydrolysis of phosphatidyl-myo-inositol 4-phosphate and phosphatidyl-myo-inositol 4,5-bisphosphate in guinea-pig synaptosomes

1978 ◽  
Vol 176 (2) ◽  
pp. 541-552 ◽  
Author(s):  
Harry D. Griffin ◽  
John N. Hawthorne
Keyword(s):  
Guinea Pig ◽  
Inositol Phosphate ◽  
Significant Loss ◽  
Ionophore A23187 ◽  
Synaptosomal Plasma Membrane ◽  
Hydrolysis Of ◽  
Guinea Pig Brain ◽  
Significant Production

1. Addition of the bivalent ionophore A23187 to synaptosomes isolated from guinea-pig brain cortex and labelled with [32P]phosphate in vitro or in vivo caused a marked loss of radioactivity from phosphatidyl-myo-inositol 4-phosphate (diphosphoinositide) and phosphatidyl-myo-inositol 4,5-bisphosphate (triphosphoinositide) and stimulated labelling of phosphatidate. No change occurred in the labelling of other phospholipids. 2. In conditions that minimized changes in internal Mg2+ concentrations, the effect of ionophore A23187 on labelling of synaptosomal di- and tri-phosphoinositide was dependent on Ca2+ and was apparent at Ca2+ concentrations in the medium as low as 10−5m. 3. An increase in internal Mg2+ concentration stimulated incorporation of [32P]phosphate into di- and tri-phosphoinositide, whereas lowering internal Mg2+ decreased labelling. 4. Increased labelling of phosphatidate was independent of medium Mg2+ concentration and apparently only partly dependent on medium Ca2+ concentration. 5. The loss of label from di- and tri-phosphoinositide caused by ionophore A23187 was accompanied by losses in the amounts of both lipids. 6. Addition of excess of EGTA to synaptosomes treated with ionophore A23187 in the presence of Ca2+ caused a rapid resynthesis of di- and tri-phosphoinositide and a further stimulation of phosphatidate labelling. 7. Addition of ionophore A23187 to synaptosomes labelled in vivo with [3H]inositol caused a significant loss of label from di- and tri-phosphoinositide, but not from phosphatidylinositol. There was a considerable rise in labelling of inositol diphosphate, a small increase in that of inositol phosphate, but no significant production of inositol triphosphate. 8. 32P-labelled di- and tri-phosphoinositides appeared to be located in the synaptosomal plasma membrane. 9. The results indicate that increased Ca2+ influx into synaptosomes markedly activates triphosphoinositide phosphatase and diphosphoinositide phosphodiesterase, but has little or no effect on phosphatidylinositol phosphodiesterase.

An ATP-inhibited soluble 5'-nucleotidase of rat kidney

1988 ◽  
Vol 254 (2) ◽  
pp. F191-F195
Author(s):  
M. Le Hir ◽  
U. C. Dubach
Keyword(s):  
High Speed ◽  
Catalytic Properties ◽  
Divalent Cations ◽  
Rat Kidney ◽  
Maximal Activity ◽  
Rate Of Hydrolysis ◽  
Membrane Bound ◽  
Ph Range ◽  
Hydrolysis Of

Hydrolysis of 5'-AMP by 5'-nucleotidase is a possible source of adenosine in the kidney. A renal membrane-bound ecto-5'-nucleotidase has been previously described. The present study deals with the catalytic properties of a 5'-AMP phosphohydrolase partially purified from high-speed supernatants of rat kidney homogenates. It exhibits phosphatase activity toward 5'-AMP, 5'-IMP, and 5'-GMP, but not toward 2'- and 3'-AMP and corresponds therefore to a 5'-nucleotidase. The hydrolysis of 5'-AMP by the soluble 5'-nucleotidase requires divalent cations. Maximal activity is reached with 10 microM of either Mn2+ or Co2+, whereas half-maximal activity is obtained with approximately 400 microM Mg2+. The soluble 5'-nucleotidase exhibits Michaelis-Menten kinetics with a Km of 9.5 microM for 5'-AMP. In the presence of 1 mM of free Mg2+, physiological concentrations of ATP provoke an increase of the Km for 5'-AMP and a decrease of Vmax. An increase of the pH of 0.4 units in the pH range 6.4-7.4 roughly doubles the rate of hydrolysis of 5'-AMP. The effects of ATP and of the pH are compatible with a role of the renal soluble 5'-nucleotidase in the hydrolysis of 5'-AMP and in the production of adenosine during hypoxia.

scholarly journals Degradation of pyrene-labelled phospholipids by lysosomal phospholipases in vitro. Dependence of degradation on the length and position of the labelled and unlabelled acyl chains

1996 ◽  
Vol 315 (3) ◽  
pp. 947-952 ◽  
Author(s):  
S Lusa ◽  
M Myllarniemi ◽  
K Volmonen ◽  
M Vauhkonen ◽  
P Somerharju
Keyword(s):  
Fatty Acid ◽  
Acyl Chain ◽  
Upward Movement ◽  
Lysosomal Degradation ◽  
Acyl Chains ◽  
Rate Of Hydrolysis ◽  
Carboxy Terminal ◽  
Hydrolysis Of

The hydrolysis of pyrenylacyl phosphatidylcholines (PyrnPCs) (n indicates the number of aliphatic carbons in the pyrene-chain) by crude lysosomal phospholipases in vitro was investigated. PyrnPCs consist of several sets in which the length of the pyrene-labelled or the unlabelled acyl chain, linked to the sn-1 or sn-2 position, was systematically varied. Lysophosphatidylcholine and fatty acid were the only fluorescent breakdown products detected, thus indicating that PyrnPCs were degraded by A-type phospholipases and lysophospholipases. Of these, mainly A1-type phospholipases appear to be involved, as determined from the relative amounts of labelled fatty acid and lysolipid released from the positional isomers. Based on the effects of the length and position of the pyrene-labelled and unlabelled chains it is suggested that (1) the lysosomal A-type phospholipases acting on PyrnPCs recognize the carboxy-terminal part of the lipid acyl chains and (2) the relevant part of the binding site is relatively narrow. Thus phospholipids with added bulk in the corresponding region, such as those that are peroxidized and polymerized, may not be good substrates for the lysosomal phospholipases mentioned. The impaired hydrolysis of the most hydrophobic PyrnPCs indicates that lysosomal phospholipases may not be able to penetrate significantly into the substrate interphase, but upward movement of the lipid may be required for efficient hydrolysis. Finally, the rate of hydrolysis of many pyrenyl derivatives was found to be comparable to that of a natural phosphatidylcholine species, both in micelles and in lipoprotein particles, indicating that these derivatives can be used as faithful reporters of lysosomal degradation of natural lipids in vivo and in vitro.

scholarly journals The hydrolysis of phosphatidylinositol monolayers at an air/water interface by the calcium-ion-dependent phosphatidylinositol phosphodiesterase of pig brain

1981 ◽  
Vol 193 (2) ◽  
pp. 607-614 ◽  
Author(s):  
K Hirasawa ◽  
R F Irvine ◽  
R M C Dawson
Keyword(s):  
Oleyl Alcohol ◽  
Enzymic Activity ◽  
Lag Phase ◽  
Water Interface ◽  
Inhibitory Effects ◽  
Pig Brain ◽  
Air Water Interface ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

1. The activity of Ca2+-dependent phosphatidylinositol phosphodiesterase (EC 3.1.4.10) of pig brain against [32P]phosphatidylinositol monolayers at an air/water interface has been measured. As the monolayer pressure was increased a sharp cut-off of enzymic hydrolysis occurred at 33 × 10(-3) N/m. 2. The addition of either phosphatidic acid, phosphatidylglycerol or oleyl alcohol increased the film pressure at which cut off occurred, as well as increasing the rate of hydrolysis at lower pressures. 3. The rate of hydrolysis, but not the cut-off pressure, was markedly increased by oleic acid and slightly increased by phosphatidylethanolamine. 4. Phosphatidylcholine, palmitoylcholine and octadecylamine decreased the cut-off pressure, as well as the enzymic activity below this pressure. 5. Stearic acid and stearyl alcohol had no effect on either the cut-off pressure or the activity. 6. All activators decreased the length of the lag phase before enzyme activity began, and phosphatidylcholine increased it. 7. These results are compared with the stimulatory and inhibitory effects of various amphiphiles observed previously with phosphatidylinositol dispersions [Irvine, Hemington & Dawson (1979) Eur. J. Biochem. 99, 525-530], and their possible relevance to the control of the phosphatidylinositol phosphodiesterase in vivo are discussed.

scholarly journals The Mood Stabilizer Valproate Inhibits both Inositol- and Diacylglycerol-signaling Pathways in Caenorhabditis elegans

2008 ◽  
Vol 19 (5) ◽  
pp. 2241-2250 ◽  
Author(s):  
Suzumi M. Tokuoka ◽  
Adolfo Saiardi ◽  
Stephen J. Nurrish
Keyword(s):  
Bipolar Disorder ◽  
Caenorhabditis Elegans ◽  
Phorbol Ester ◽  
Acetylcholine Release ◽  
Inositol Phosphate ◽  
Mood Stabilizer ◽  
Egg Laying ◽  
Inositol 1 ◽  
Inositol 1,4,5 Trisphosphate ◽  
Hydrolysis Of

The antiepileptic valproate (VPA) is widely used in the treatment of bipolar disorder, although the mechanism of its action in the disorder is unclear. We show here that VPA inhibits both inositol phosphate and diacylglycerol (DAG) signaling in Caenorhabditis elegans. VPA disrupts two behaviors regulated by the inositol-1,4,5-trisphosphate (IP3): defecation and ovulation. VPA also inhibits two activities regulated by DAG signaling: acetylcholine release and egg laying. The effects of VPA on DAG signaling are relieved by phorbol ester, a DAG analogue, suggesting that VPA acts to inhibit DAG production. VPA reduces levels of DAG and inositol-1-phosphate, but phosphatidylinositol-4,5-bisphosphate (PIP2) is slightly increased, suggesting that phospholipase C-mediated hydrolysis of PIP2 to form DAG and IP3 is defective in the presence of VPA.

Sign in / Sign up

Export Citation Format

Share Document