scholarly journals Effect of hypoxia on phosphatidylcholine biosynthesis in the isolated hamster heart

1990 ◽  
Vol 268 (1) ◽  
pp. 47-54 ◽  
Author(s):  
G M Hatch ◽  
P C Choy
Keyword(s):  
Active Form ◽  
Compensatory Mechanism ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Hypoxic Conditions ◽  
Rate Limiting Step ◽  
Phosphatidylcholine Biosynthesis ◽  
Hamster Heart ◽  
Rate Limiting ◽  
Hypoxic Treatment

In hamster heart, the majority of the phosphatidylcholine is synthesized via the CDP-choline pathway, and the rate-limiting step of this pathway is catalysed by CTP:phosphocholine cytidylyltransferase (EC 2.7.7.15). We have shown previously [Choy (1982) J. Biol. Chem. 257, 10928-10933] that, in the myopathic heart, the level of cardiac CTP was diminished during the development of the disease. In order to maintain the level of CDP-choline, and consequently the rate of phosphatidylcholine biosynthesis, cardiac cytidylyltransferase activity was increased. However, it was not clear if the same compensatory mechanism would occur when the cardiac CTP level was decreased rapidly. In this study, hypoxia of the hamster heart was produced by perfusion with buffer saturated with 95% N2. The heart was pulse-labelled with radioactive choline and then chased with non-radioactive choline for various periods under hypoxic conditions. There was a severe decrease in ATP and CTP levels within 60 min of hypoxic perfusion, with a corresponding fall in the rate of phosphatidylcholine biosynthesis. Analysis of the choline-containing metabolites revealed that the lowered ATP level did not affect the phosphorylation of choline to phosphocholine, but the lower CTP level resulted in the decreased conversion of phosphocholine to CDP-choline. Determination of enzyme activities revealed that hypoxic treatment resulted in the enhanced translocation of cytidylyltransferase from the cytosolic to the microsomal form. This enhanced translocation was probably caused by the accumulation of fatty acids in the heart during hypoxia. We postulate that the enhancement of translocation of the cytidylyltransferase to the microsomal form (a more active form) is a mechanism by which the heart can compensate for the decrease in CTP level during hypoxia in order to maintain phosphatidylcholine biosynthesis.

Effect of cAMP on choline uptake and phosphatidylcholine biosynthesis in cultured chick heart cells

1988 ◽  
Vol 66 (3) ◽  
pp. 231-237 ◽  
Author(s):  
Paul S. Sunga ◽  
P. Haydn Pritchard ◽  
Simon W. Rabkin
Keyword(s):  
Phosphodiesterase Inhibitor ◽  
Cardiac Cells ◽  
Heart Cells ◽  
Choline Uptake ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Phosphatidylcholine Biosynthesis ◽  
Chick Heart ◽  
Rate Limiting

The effect of an analogue of cAMP on the uptake and metabolism of choline in the heart was studied in isolated cardiac cells. The cells were obtained from 7-day-old chick embryos and maintained in culture. The effects of cAMP were studied using the dibutyryl cAMP analogue and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. After a 2-h incubation with [3H]choline, about 85% of the label was recovered in phosphocholine, with most of the rest in phospholipid. During a subsequent chase incubation, [3H]phosphocholine was transferred to phosphatidylcholine with little accumulation in CDP-choline. This suggests the rate-limiting step for the conversion of phosphocholine to phosphatidylcholine in these cells is the synthesis of CDP-choline. cAMP decreased the incorporation of choline into phosphatidylcholine, but did not change the flux of metabolites through the step catalyzed by CTP:phosphocholine cytidylyltransferase. cAMP had little effect on choline uptake at low (1–25 μM) extracellular choline concentrations, but significantly (p < 0.05) decreased choline uptake at higher (37.5–50 μM) extracellular choline concentrations. Thus, cardiac cells take up and metabolize choline to phosphocholine, with CTP:phosphocholine cytidylyltransferase being the rate-limiting step in phosphatidylcholine biosynthesis. cAMP decreases [3H]choline uptake and its subsequent incorporation into phosphocholine and phospholipid. However, the metabolism of choline within the cell is unaffected.

Regulation of phosphatidylcholine metabolism in mammalian hearts

1989 ◽  
Vol 67 (2-3) ◽  
pp. 67-77 ◽  
Author(s):  
Grant M. Hatch ◽  
Karmin O ◽  
Patrick C. Choy
Keyword(s):  
Phospholipase A ◽  
Current Evidence ◽  
Major Phospholipid ◽  
Mammalian Heart ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Phosphatidylcholine Biosynthesis ◽  
Rate Limiting ◽  
Phosphatidylcholine Metabolism

Phosphatidylcholine is the major phospholipid in the mammalian heart. Over 90% of the cardiac phosphatidylcholine is synthesized via the CDP-choline pathway. The rate-limiting step of this pathway is catalyzed by CTP:phosphocholine cytidylyltransferase. Current evidence suggests that phosphatidylcholine biosynthesis in the heart is regulated by the availability of CTP and the modulation of cytidylyltransferase activity. Phosphatidylcholine is degraded mainly by the actions of phospholipase A1 and A2, with the formation of lysophosphatidylcholine. Lysophosphatidylcholine may be further deacylated by lysophospholipase or reacylated back into the parent phospholipid by the action of acyltransferase. The accumulation of lysophosphatidylcholine in the heart may be one of the biochemical factors for the production of cardiac arrhythmias.Key words: phosphatidylcholine, phospholipids, biosynthesis, metabolism, heart.

scholarly journals DETERMINATION OF l-HISTIDINE IN NANOGRAM AMOUNTS AND THE QUESTION OF ITS OCCURRENCE IN MAST CELLS

1972 ◽  
Vol 20 (11) ◽  
pp. 917-922 ◽  
Author(s):  
DAVID I. WILKINSON ◽  
DAVID GLICK
Keyword(s):  
Mast Cells ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Peritoneal Mast Cells ◽  
Before And After ◽  
Chromatographic Detection ◽  
Rat Peritoneal Mast Cells ◽  
Rate Limiting

In an attempt to clarify the question of whether histidine is stored in the mast cell for coversion to histamine or whether the rate of conversion is rapid enough to prevent accumulation of histidine so that the rate-limiting step is the histidine uptake, it was found that no histidine was demonstrable in rat peritoneal mast cells by either quantitative analysis or paper chromatographic detection. Microadaptation of Hassall's method, based on conversion of l-histidine by histidase to urocanic acid and measurement of the latter by its absorbance at 277 nm, was made to permit determination of histidine in nanogram amounts in the presence of histamine. This adaptation was found reliable when compared with the o-phthalaldehyde method in estimation of l-histidine in serum and in insulin hydrolysate, and then it was applied to analysis of mast cells before and after l-histidine uptake in vitro. The adaptation should be generally useful in microanalysis of l-histidine in histologically and cytologically defined samples.

Choline glycerophospholipid biosynthesis in the guinea pig heart

1987 ◽  
Vol 65 (10) ◽  
pp. 860-868 ◽  
Author(s):  
Monika Wientzek ◽  
Ricky Y. K. Man ◽  
Patrick C. Choy
Keyword(s):  
Guinea Pig ◽  
Choline Kinase ◽  
Major Pathway ◽  
Guinea Pig Heart ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Choline Glycerophospholipids ◽  
Mammalian Liver ◽  
Rate Limiting

The aims of this study were to (i) elucidate the biosynthetic pathways for the formation of plasmenylcholine in the mammalian heart and (ii) investigate whether the control of choline glycerophospholipid production is different in hearts with high plasmenylcholine content. Guinea pig hearts were used throughout this study, since 34% of the cardiac choline glycerophospholipids in this species is present in the plasmenylcholine form. By perfusion of the guinea pig heart in the Langendorff mode with labeled choline, we demonstrated that the majority of plasmenylcholine in the heart was synthesized via the CDP-choline pathway. The ability of the heart to form plasmenylcholine from CDP-choline and 1-alkenyl-2-acylglycerol was also shown. We postulate that 1-alkenyl-2-acylglycerol in the guinea pig heart might originate from the hydrolysis of plasmenylethanolamine. In mammalian liver and other tissues, the CDP-choline pathway is the major pathway for phosphatidylcholine biosynthesis and the rate-limiting step is catalyzed by CTP:phosphocholine cytidylyltransferase. The results obtained from the present study support this supposition. In addition, evidence was obtained indicating that phosphorylation of choline by choline kinase in the CDP-choline pathway may also be rate limiting. Although the involvement of choline kinase as a rate-limiting enzyme in the CDP-choline pathway has been shown in a number of cell cultures, the rate-limiting role of this enzyme in intact mammalian organs has not been previously reported. The rationale for the presence of more than one rate-limiting step in the CDP-choline pathway in the guinea pig heart remains undefined.

Determination of the Isotope Effect of the Enzymatic Oxidation of (R)Carnitine by Displacement of the Equilibrium via Mass Action

1975 ◽  
Vol 30 (7-8) ◽  
pp. 438-441
Author(s):  
Klaus Brendel ◽  
Rubin Bressler ◽  
Miguel A. Alizade
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Isotope Effect ◽  
Mass Action ◽  
Enzymatic Oxidation ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Different Temperatures ◽  
Acid Hydrochloride ◽  
Rate Limiting

Abstract An isotope effect of the dehydrogenation of (R) Carnitine [(R) 3-hydroxy-4-trimethylamino-butyric acid hydrochloride] catalyzed by (R) carnitine dehydrogenase [(R) carnitine: NAD oxido-reductase E.C. 1.1.1.108] from Pseudomonas aeruginosa was measured at different temperatures. It was found that k1H/k3H does not vary greatly with changes of temperature. The value of 3 for k1H/k3H measured at small initial conversions strongly indicated that the rate limiting step of the oxidation of (R) carnitine is the cleavage of the C-H bond at C3.

Three factors that modulate the activity of class D β-lactamases and interfere with the post-translational carboxylation of Lys70

2010 ◽  
Vol 432 (3) ◽  
pp. 495-506 ◽  
Author(s):  
Lionel Vercheval ◽  
Cédric Bauvois ◽  
Alexandre di Paolo ◽  
Franck Borel ◽  
Jean-Luc Ferrer ◽  
...  
Keyword(s):  
Active Site ◽  
Chloride Ions ◽  
Side Chain ◽  
Wild Type ◽  
Post Translational Modification ◽  
Rate Limiting Step ◽  
Class D ◽  
The Individual ◽  
Rate Limiting

The activity of class D β-lactamases is dependent on Lys70 carboxylation in the active site. Structural, kinetic and affinity studies show that this post-translational modification can be affected by the presence of a poor substrate such as moxalactam but also by the V117T substitution. Val117 is a strictly conserved hydrophobic residue located in the active site. In addition, inhibition of class D β-lactamases by chloride ions is due to a competition between the side chain carboxylate of the modified Lys70 and chloride ions. Determination of the individual kinetic constants shows that the deacylation of the acyl–enzyme is the rate-limiting step for the wild-type OXA-10 β-lactamase.

scholarly journals The regulation of phosphatidylcholine biosynthesis in rye (Secale cereale) roots. Stimulation of the nucleotide pathway by low temperature

1987 ◽  
Vol 242 (3) ◽  
pp. 755-759 ◽  
Author(s):  
A J Kinney ◽  
D T Clarkson ◽  
B C Loughman
Keyword(s):  
Secale Cereale ◽  
Choline Chloride ◽  
Rate Limiting Step ◽  
Phosphatidylcholine Biosynthesis ◽  
Secale Cereale L ◽  
Choline Phosphate ◽  
Relative Differences ◽  
Rate Limiting

The incorporation of [14C]choline chloride and [14C]glycerol into segments taken from rye (Secale cereale L., cv. Rheidal) roots was greater in segments from roots grown at 5 degrees C than in segments taken from roots growing at 20 degrees C. The incorporation was measured at the temperature at which the root had been growing. Measurements in vitro of the enzymes of the nucleotide pathway showed activity of choline kinase (EC 2.7.1.32), choline-phosphate cytidylyltransferase (EC 2.7.7.15) and cholinephosphotransferase (EC 2.7.8.2) to be higher in homogenates from the cooler roots when assayed at 5 degrees C than the activities assayed at 20 degrees C in the 20 degrees C-root homogenates. Changes in vivo in the pool sizes of the CDP-base intermediates with temperature, relative differences in nucleotide-pathway-enzyme activities and a pulse-chase experiment with [14C]choline indicated that the rate-limiting step for phosphatidylcholine biosynthesis in this tissue, at both temperatures, was the reaction catalysed by cytidylyltransferase.

Effects of fatty acids on phosphatidylcholine biosynthesis in isolated hamster heart

1986 ◽  
Vol 64 (5) ◽  
pp. 413-417 ◽  
Author(s):  
Thomas Mock ◽  
Tracy L. Slater ◽  
Gilbert Arthur ◽  
Alvin C. Chan ◽  
Patrick C. Choy
Keyword(s):  
Fatty Acids ◽  
Stearic Acid ◽  
Microsomal Fraction ◽  
Rat Hepatocytes ◽  
Free Form ◽  
Ctp:Phosphocholine Cytidylyltransferase ◽  
Phosphatidylcholine Biosynthesis ◽  
Hamster Heart ◽  
Arachidonic Acids

The effects of stearic, oleic, and arachidonic acids on phosphatidylcholine biosynthesis in the hamster heart were investigated. When hamster hearts were perfused with labelled choline in the presence of fatty acids, biosynthesis of phosphatidylcholine was stimulated only by stearic acid. Stearic acid was found to accumulate in unesterified (free) form in the hamster heart after perfusion. The stimulation by stearic acid was mediated in vivo by an enhancement of CTP:phosphocholine cytidylyltransferase activity in the microsomal fraction of the hamster heart and the enzyme activity in the cytosolic fraction was not affected. In contrast with the observations in rat hepatocytes, cytidylyltransferase from the hamster heart was not stimulated directly by stearic acid. The selective activation of the microsomal enzyme when the heart was perfused with stearic acid suggests that activation of the enzyme was mediated via the modification of the membrane by stearic acid.

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