scholarly journals The action of phosphatidylinositol-specific phospholipases C on membranes

1976 ◽  
Vol 154 (1) ◽  
pp. 203-208 ◽  
Author(s):  
M G Low ◽  
J B Finean
Keyword(s):  
Phospholipase C ◽  
Rat Liver ◽  
Microsomal Fraction ◽  
Phosphatidyl Inositol ◽  
Detectable Effect ◽  
Erythrocyte Ghosts ◽  
Membrane Phospholipids ◽  
Liver Microsomal Fraction ◽  
Hydrolysis Of ◽  
Low Activity

A phospholipase C prepared from lymphocytes readily hydrolysed pure phosphatidyl-inositol but was relatively ineffective against phosphatidylinositol in erythrocyte “ghosts” and rat liver microsomal fraction and also against sonicated lipid extracts from these membranes. In contrast, a phospholipase C prepared from Staphylcoccus aureus readily hydrolysed phosphatidylinositol in sonicated lipid extracts but had only low activity against purified phosphatidylinositol. Unlike the enzyme from lymphocytes, the S. aureus phospholipase C did not require Ca2+ for its activity and was inhibited by cations. The previously reported specificity of this enzyme was confirmed by our observation of hydrolysis of approx. 75% of the phosphatidylinositol in ox, sheep and cat erythrocyte “ghosts” together with no detectable effect on the major erythrocyte membrane phospholipids. The phosphatidylinositol of rat liver microsomal fraction was hydrolysed only to a maximum of 15%. Some preliminary experiments showed that approx. 60% of the phosphatidylinositol of ox or sheep erythrocytes could be hydrolysed without causing substantial haemolysis.

scholarly journals Hydrolysis of membrane phospholipids by phospholipases of rat liver lysosomes

1979 ◽  
Vol 182 (2) ◽  
pp. 599-606 ◽  
Author(s):  
Donald E. Richards ◽  
Robin F. Irvine ◽  
Rex M. C. Dawson
Keyword(s):  
Phospholipase C ◽  
Rat Liver ◽  
Lysosomal Enzymes ◽  
Microsomal Fraction ◽  
Water Soluble ◽  
Membrane Phospholipids ◽  
Liver Lysosomes ◽  
Rat Liver Lysosomes ◽  
Hydrolysis Of

(1) The hydrolysis of 32P- or myo-[2-3H]inositol-labelled rat liver microsomal phospholipids by rat liver lysosomal enzymes has been studied. (2) The relative rates of hydrolysis of phospholipids at pH4.5 are: sphingomyelin>phosphatidylethanolamine>phosphatidylcholine> phosphatidylinositol. (3) The predominant products of phosphatidylcholine and phosphatidylethanolamine hydrolysis are their corresponding lyso-compounds, indicating a slow rate of total deacylation. (4) Ca2+ inhibits the hydrolysis of all phospholipids, though only appreciably at high (>5mm) concentration. The hydrolysis of sphingomyelin is considerably less sensitive to Ca2+ than that of glycerophospholipids. (5) Analysis of the water-soluble products of phosphatidylinositol hydrolysis (by using myo-[3H]inositol-labelled microsomal fraction as a substrate) produced evidence that more than 95% of the product is phosphoinositol, which was derived by direct cleavage from phosphatidylinositol, rather than by hydrolysis of glycerophosphoinositol. (6) This production of phosphoinositol, allied with negligible lysophosphatidylinositol formation and a detectable accumulation of diacylglycerol, indicates that lysosomes hydrolyse membrane phosphatidylinositol almost exclusively in a phospholipase C-like manner. (7) Comparisons are drawn between the hydrolysis by lysosomal enzymes of membrane substrates and that of pure phospholipid substrates, and also the possible role of phosphatidylinositol-specific lysosomal phospholipase C in cellular phosphatidylinositol catabolism is discussed.

scholarly journals The hydrolysis of phosphatidylinositol by lysosomal enzymes of rat liver and brain

1978 ◽  
Vol 176 (2) ◽  
pp. 475-484 ◽  
Author(s):  
R F Irvine ◽  
N Hemington ◽  
R M C Dawson
Keyword(s):  
Phospholipase C ◽  
Rat Liver ◽  
Gel Filtration ◽  
Phosphatidyl Inositol ◽  
Temperature Stability ◽  
Enzyme Systems ◽  
Phosphatidic Acid Phosphatase ◽  
Bivalent Metals ◽  
Hydrolysis Of ◽  
Marked Specificity

1. Lysosomes from rat liver contain two enzymic systems for hydrolysing phosphatidyl-inositol: a deacylation via lysophosphatidylinositol producing glycerophosphoinositol and non-esterified fatty acid, and a phospholipase C-like cleavage into inositol 1-phosphate and diaclygycerol. 2. The separate enzyme systems involved can be distinguished by gel filtration, differential temperature-stability and the inhibitory action of detergents. 3. The enzyme systems both have pH optima at 4.8 and their attack on a pure phosphatidylinositol substrate is inhibited by many bivalent metals including Ca2+ and Mg2+, and cationic drugs. 4. Whereas the deacylation system will attack other glycerophospholipids, the phospholipase C shows a marked specificity towards phosphatidylinositol, although it will also slowly attach phosphatidylcholine with the liberation of phosphocholine. 5. Gel filtration and temperature-stability distinguish the phospholipase C from lysosomal phosphatidic acid phosphatase, but not from sphingomyelinase. 6. Evidence is presented that an EDTA-insensitive phospholipase C degrading phosphatidylinositol is present in rat brain.

scholarly journals Binding of inositol trisphosphate by a liver microsomal fraction

1986 ◽  
Vol 233 (3) ◽  
pp. 929-932 ◽  
Author(s):  
A Spät ◽  
A Fabiato ◽  
R P Rubin
Keyword(s):  
Binding Site ◽  
Phospholipase C ◽  
Rat Liver ◽  
Receptor Binding ◽  
Microsomal Fraction ◽  
Inositol Trisphosphate ◽  
Specific Receptor ◽  
Receptor Binding Site ◽  
Inositol 1,4,5 Trisphosphate ◽  
Liver Microsomal Fraction

Accumulating evidence suggests that the increase in cytosolic Ca2+ induced by receptor agonists is mediated by inositol 1,4,5-trisphosphate, a product of phospholipase C-mediated breakdown of phosphatidylinositol 4,5-bisphosphate. The present study employs inositol tris[32P]phosphate to demonstrate a specific receptor binding site in a microsomal fraction of rat liver.

Influence of 1,4-benzdiazepin-2-ones on rat liver microsomal fraction and hepatocytes

1987 ◽  
Vol 21 (1) ◽  
pp. 5-8
Author(s):  
T. I. Davidenko ◽  
O. V. Sevast'yanov ◽  
L. N. Yakubovskaya
Keyword(s):  
Rat Liver ◽  
Microsomal Fraction ◽  
Liver Microsomal Fraction

scholarly journals Loss of haem in rat liver caused by the porphyrogenic agent 2-allyl-2-isopropylacetamide

1971 ◽  
Vol 124 (4) ◽  
pp. 767-777 ◽  
Author(s):  
F. De Matteis
Keyword(s):  
Rat Liver ◽  
Microsomal Fraction ◽  
Direct Evidence ◽  
Gradual Increase ◽  
Rapid Loss ◽  
Metabolizing Enzymes ◽  
Liver Microsomal Fraction ◽  
Green Pigments ◽  
Cytochrome P 450 ◽  
Increased Activity

1. The effect of a single dose of 2-allyl-2-isopropylacetamide on the cytochrome P-450 concentration in rat liver microsomal fraction was studied. The drug caused a rapid loss of cytochrome P-450 followed by a gradual increase to above the normal concentration. 2. The loss of cytochrome P-450 was accompanied by a loss of microsomal haem and by a brown–green discoloration of the microsomal fraction suggesting that a change in the chemical constitution of the lost haem had taken place. Direct evidence for this was obtained by prelabelling the liver haems with radioactive 5-aminolaevulate: the drug caused a loss of radioactivity from the haem with an increase of radioactivity in a fraction containing certain un-identified green pigments. 3. Evidence was obtained by a dual-isotopic procedure that rapidly turning-over haem(s) may be preferentially affected. 4. The loss of cytochrome P-450 as well as the loss of microsomal haem and the discoloration of the microsomal fraction were more intense in animals pretreated with phenobarbitone and were much less evident when compound SKF 525-A (2-diethylaminoethyl 3,3-diphenylpropylacetate) was given before 2-allyl-2-isopropylacetamide, suggesting that the activity of the drug-metabolizing enzymes may be involved in these effects. 5. The relevance of the destruction of liver haem to the increased activity of 5-aminolaevulate synthetase caused by 2-allyl-2-isopropylacetamide is discussed.

scholarly journals Effect of Phospholipase C Hydrolysis of Membrane Phospholipids on Membranous Enzymes

1972 ◽  
Vol 247 (9) ◽  
pp. 2835-2841 ◽  
Author(s):  
Richard D. Mavis ◽  
Robert M. Bell ◽  
P. Roy Vagelos
Keyword(s):  
Phospholipase C ◽  
Membrane Phospholipids ◽  
Hydrolysis Of

scholarly journals Fatty acid stimulation of membrane phosphatidylinositol hydrolysis by brain phosphatidylinositol phosphodiesterase

1979 ◽  
Vol 178 (2) ◽  
pp. 497-500 ◽  
Author(s):  
R F Irvine ◽  
A J Letcher ◽  
R M Dawson
Keyword(s):  
Arachidonic Acid ◽  
Oleic Acid ◽  
Fatty Acid ◽  
Acid Content ◽  
Microsomal Fraction ◽  
Fatty Acid Content ◽  
Membrane Bound ◽  
Liver Microsomal Fraction ◽  
Hydrolysis Of ◽  
Stimulation Of

The hydrolysis of membrane-bound phosphatidylinositol in rat liver microsomal fraction by the soluble phosphatidylinositol phosphodiesterase from rat brain was markedly stimulated by oleic acid or arachidonic acid. The stimulation did not require added calcium, although it was abolished by EDTA. Lysophosphatidylcholine also totally suppressed the stimulation. A possible role for the fatty acid content of a membrane in controlling phosphatidylinositol turnover is suggested.

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