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Phosphoinositides and PIPs

Phosphoinositides and PIPs

Phosphoinositides are a group of phospholipids containing a glycerol backbone with two fatty acid chains and a phosphate attached to a myoinositol sugar ring. The inositol head group extends into the cytoplasm, where it is modified by adding phosphate groups to form phosphatidylinositol phosphates or PIPs.
Different phosphoinositides are synthesized and recruited on the cytosolic face of the plasma membrane. The localization of specific phosphoinositides concentrated in separate membrane...

Assembly of the Lipid Bilayer in the ER

Assembly of the Lipid Bilayer in the ER

Biological membranes are more than just a barrier separating cell cytoplasm from the outside environment. They are highly dynamic and help maintain the integrity and physiological stability of the cells as well as membrane-bound organelles. Membranes also play vital roles in cell-to-cell and intracellular communication.
A large chunk of any biological membrane is composed of phospholipids. These lipids have a heterogeneous distribution across different subcellular organelles and even between...

Membrane Asymmetry Regulating Transporters

Membrane Asymmetry Regulating Transporters

Enzymes like flippase, floppase, and scramblase transfer phospholipids from one layer to another in the membrane, thereby affecting membrane asymmetry.
Flippase
Eukaryotic flippases are type-IV P-type ATPases or P4-ATPases belonging to P-type ATPase family proteins that are membrane-bound pumps involved in the ATP-mediated transport of ions and molecules across the membrane. Flippases flip specific phospholipids from the outer to the inner leaflet of a membrane. All P4-ATPases have one...

Amplifying Signals via Second Messengers

Amplifying Signals via Second Messengers

Many receptor binding ligands are hydrophilic; they do not cross the cell membrane but bind to cell-surface receptors. Thus, their message must be relayed by second messengers present in the cell cytoplasm. There are several second messenger pathways, each with its own way of relaying information. For example, the G protein-coupled receptors can activate both phosphoinositol and cyclic AMP (cAMP) second messenger pathways. The phosphoinositol pathway is active when the receptor induces...

Amplifying Signals via Enzymatic Cascade

Amplifying Signals via Enzymatic Cascade

When a ligand binds to a cell-surface receptor, the receptor's intracellular domain changes shape, which may either activate its enzyme function or allow its binding to other molecules. The initial signal is amplified by most signal transduction pathways. This means that a single ligand molecule can activate multiple molecules of a downstream target. Proteins that relay a signal are most commonly phosphorylated at one or more sites, activating or inactivating the protein. Kinases catalyze the...

IP3/DAG Signaling Pathway

IP3/DAG Signaling Pathway

Membrane lipids such as phosphatidylinositol (PI) are precursors for several membrane-bound and soluble second messengers. Specific kinases phosphorylate PI and produce phosphorylated inositol phospholipids. One such inositol phospholipids are the phosphatidylinositol-4,5 bisphosphate [PI(4,5)P2], present in the inner half of the lipid bilayer. Upon ligand binding, GPCR stimulates Gq proteins to turn on phospholipase Cꞵ. Activated phospholipase Cꞵ cleaves PI(4,5)P2 and produces two-second...

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Related Experiment Video

Updated: Jul 22, 2026

A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins

A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins

Published on: March 22, 2012

Phospholipid scramblase activation pathways in lymphocytes.

P Williamson¹, A Christie, T Kohlin

¹Department of Biology, Amherst College, Amherst, Massachusetts 01002, USA.

|July 4, 2001

Summary

Calcium and apoptosis activate the same lipid scramblase in lymphoid cells through distinct pathways. This enzyme facilitates rapid phospholipid movement, crucial for cell function and apoptosis.

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Last Updated: Jul 22, 2026

A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins

A TIRF Microscopy Technique for Real-time, Simultaneous Imaging of the TCR and its Associated Signaling Proteins

Published on: March 22, 2012

Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes

Static Adhesion Assay for the Study of Integrin Activation in T Lymphocytes

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A Fluorescence-based Assay of Phospholipid Scramblase Activity

A Fluorescence-based Assay of Phospholipid Scramblase Activity

Published on: September 20, 2016

Area of Science:

Cell Biology
Biochemistry
Membrane Transport

Background:

The scramblase enzyme facilitates rapid, bidirectional transbilayer movement of phospholipids across cell membranes.
This activity is well-characterized in erythrocytes and platelets but less understood in lymphoid cells.

Purpose of the Study:

To investigate the activation mechanisms and kinetics of scramblase in lymphoid cells.
To compare scramblase activation by intracellular calcium (Ca2+) and apoptosis.

Main Methods:

Scramblase assays were performed on lymphoid cells.
Intracellular Ca2+ levels were manipulated to induce scrambling.
Apoptosis was induced to observe its effect on scramblase activity.
Lymphoid cells from a patient with Scott syndrome were analyzed.

Main Results:

Lymphoid cells exhibit scramblase activity with rates intermediate between platelets and erythrocytes.
Scramblase activation by Ca2+ in lymphoid cells shows a lag phase not observed in other cell types.
Both Ca2+ and apoptosis activate scramblase, but Ca2+ activation is impaired in Scott syndrome cells.
The rate of lipid movement is similar whether activated by Ca2+ or apoptosis, and Ca2+ elevation does not additively increase scrambling in apoptotic cells.

Conclusions:

Calcium and apoptosis activate the same lipid scramblase in lymphoid cells.
These two stimuli likely utilize different signaling pathways to converge on the same scramblase.
Scramblase plays a critical role in phospholipid dynamics during cellular stress and apoptosis in lymphoid cells.