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Biochimica et biophysica acta1983; 752(2); 329-338; doi: 10.1016/0005-2760(83)90131-5

Properties and distribution of phosphatidylinositol-specific phospholipase C in human and horse platelets.

Abstract: Phospholipase C has been studied in homogenates, total particulate and soluble fractions of horse and human platelets. This enzyme, assayed with exogenous L-3-phosphatidyl[14C]inositol, is predominantly localized in the soluble fraction and its distribution parallels that of lactate dehydrogenase. A small percentage of activity present in the particulate fraction seems to be due to contamination with soluble enzyme. Enzyme from horse and human platelets appears identical, having a Km of 0.10-0.15 mM, acid pH optimum (pH 5.5) and showing Ca2+-dependency and weak inhibition by deoxycholate. Analysis of the reaction products shows the formation of myo-inositol 1,2-cyclic phosphate and myo-inositol 1-phosphate in almost equal amounts. Platelet stimulation with thrombin does not seem to induce association of the cytosolic activity to the membranes. The cytosolic activity is not affected by pretreatment of the intact platelets with prostacyclin or thrombin. Degradation of phosphatidylinositol present in a membrane fraction isolated from platelets by cytosolic phospholipase C requires addition of deoxycholate. Our information suggests that the degradation of phosphatidylinositol in stimulated platelets is mainly achieved by exposure of the substrate to the cytosolic enzyme and by an increase of the free Ca2+ concentration needed for optimal phospholipase C activity.
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Publication Date: 1983-07-12 PubMed ID: 6860706DOI: 10.1016/0005-2760(83)90131-5Google Scholar: Lookup
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  • Journal Article
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  • Non-U.S. Gov't

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The paper deals with the investigation of an enzyme known as Phospholipase C in horse and human blood platelets, focusing on its properties, distribution, and activities.

Overview of Research

In this research, scientists studied Phospholipase C in horse and human platelets. The enzyme was tested with exogenous L-3-phosphatidyl[14C]inositol and was mostly found in the soluble fraction, much like lactate dehydrogenase. Most notably, they found that this enzyme operation is not influenced by prostacyclin or thrombin pre-exposure.

  • The study covers the properties and distribution of Phospholipase C in different components, such as homogenates, total particulate, and soluble parts of the platelets in both humans and horses.
  • For the study, the enzyme was assessed using exogenous L-3-phosphatidyl[14C]inositol. It was primarily located in the soluble part, and its distribution was parallel to that of enzyme lactate dehydrogenase (LDH).
  • A small amount of enzymatic activity was noted in the particulate fraction, which researchers suggested could likely be due to contamination from the soluble enzyme component.

Phospholipase C from Human and Horse Platelets

The enzyme phospholipase C from horse and human platelets seem to share identical properties.

  • Both enzymes have the same Km value of 0.10-0.15 mM, indicating the same binding affinity for their molecules.
  • Both have an optimal activity at an acid pH of 5.5 and are calcium-dependent. This means they function best under slightly acidic conditions and require calcium to be present for optimal enzymatic activity.
  • They both showed weak inhibition to deoxycholate, which inhibits the overall enzyme functionality.
  • When analyzed, the products of the reaction were mainly myo-inositol 1,2-cyclic phosphate and myo-inositol 1-phosphate, roughly in equal proportions.

Effects from Stimuli on Phospholipase C

In this study, the researchers observed how the enzyme’s functionality changed when influenced by stimuli like thrombin and prostacyclin.

  • Stimulating platelets with thrombin didn’t seem to increase the association of the enzyme’s activity from the cytosol (liquid part inside cells) to the membranes.
  • This cytosolic activity of the phospholipase C also didn’t change when platelets were pretreated with prostacyclin or thrombin.
  • The enzyme’s ability to degrade phosphatidylinositol (a type of fat molecule in cell membranes) in membrane fractions required the addition of deoxycholate.
  • The degradation of phosphatidylinositol in activated platelets is thought to be mainly due to the exposure of the substrate to the cytosolic enzyme, along with an increase in free calcium concentration – vital for optimal phospholipase C activity.

Cite This Article

APA
Siess W, Lapetina EG. (1983). Properties and distribution of phosphatidylinositol-specific phospholipase C in human and horse platelets. Biochim Biophys Acta, 752(2), 329-338. https://doi.org/10.1016/0005-2760(83)90131-5

Publication

Biochimica et biophysica acta
ISSN: 0006-3002
NlmUniqueID: 0217513
Country: Netherlands
Language: English
Volume: 752
Issue: 2
Pages: 329-338

Researcher Affiliations

Siess, W
    Lapetina, E G

      MeSH Terms

      • Animals
      • Blood Platelets / enzymology
      • Cell Membrane / enzymology
      • Chemical Phenomena
      • Chemistry
      • Cytosol / enzymology
      • Horses
      • Humans
      • L-Lactate Dehydrogenase / blood
      • Phosphatidylinositols / blood
      • Phospholipases / blood
      • Solubility
      • Species Specificity
      • Subcellular Fractions / enzymology
      • Type C Phospholipases / blood

      Citations

      This article has been cited 15 times.
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