Phospholipid Metabolism in Cellular Signaling

Jose M. Mato

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315896427
• eBook ISBN: 9781351092425
• Edition: 1
• Topic: Medicine
• Subtopic: Biochemistry in Medicine

Phospholipids are no longer considered exclusively as the building blocks of biomembranes, but are now regarded to be exceptionally important to cellular signalling.Another conclusion resulting from studies over the past several years is that no single general scheme for the role of phospholipids during cell activation can be drawn as representative of all cells. This book presents a comprehensive view of the recent advances made in certain major research areas within the field of phospholipid metabolism in cellular signalling. Topics discussed within this volume include lipid composition of cellular membranes and their organization in biological systems, the dynamic aspects of phospholipid metabolism and its regulation by extracellular stimuli, and the role of newly discovered glycosyl-phosphatidylinositols in insulin action. The book also discusses two biologically active phospholipids: the sphingolipids, and ether-linked glycerophospholipids (the platelet activating factor). Phospholipid Metabolism in Cellular Signaling is an important research reference that should be considered required reading by all scientists and graduate students working on cell activation (e.g., growth factors, hormones, and oncogenes).

Chapter 1
Lipid Components of Cellular Membranes

José M. Mato

Table of Contents

I.	Membrane Components
II.	Lipid Components of Cellular Membranes
	A. General Information
	B. Glycerophospholipids
	C. Sphingolipids
	D. Glycosphingolipids
References

I. Membrane Components

All cell membranes consists mostly of an association of lipids and proteins. The proportion of both components differs between different membranes and is not even constant in time for a given membrane. Table 1 shows the ratio of protein to lipid for various rat liver membranes.¹ Whereas plasma membranes isolated from rat liver have a protein/lipid ratio of about 1.5, this same ratio in the inner membrane of mitochondria is 3.6. These differences are due to the specific functions that each membrane plays within the cell. As a general rule, membranes which are metabolically more active contain a higher proportion of protein. Certain proteins or lipids are almost exclusively associated with one type of membrane and do not appear in other morphologically different membranes. These specific components are therefore "membrane markers" and can be used to assess the purity of particular membrane fractions. Membrane markers most commonly used possess enzyme activity. Some of the enzyme activities commonly used during purification of rat liver membranes are shown in Table 2. Several lipids are plasma membrane markers. Thus, the phosphoinositides phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate and the galactosides are almost exclusively localized in the plasma membrane.^2-4 Mitochondrial membranes are characterized by the presence of diphosphatidylglycerol, which is mainly located in the inner membrane of this subcellular fraction. The relative amount of a given marker (protein or lipid) might vary during the life cycle of the cell. These changes are associated with the various functions of a given membrane during the life cycle of the cell.

In addition to the lipid and protein, biological membranes contain carboydrates (up to 10% of their dry weight), water (about 20% of the total mass), and magnesium, calcium, and other ions. Carbohydrates are preferentially found on the cell surface, where they are covalently associated with proteins and lipids.

II. Lipid Components of Cellular Membranes

A. General Information

The hydrophobic nature of cell membranes is due to the lipid components, which are water insoluble. Four major classes of lipids can be distinguished in eukaryotic cell membranes: glycerophospholipids, sphingolipids, glycosphingolipids, and sterols. Glycerophospholipids and sphingolipids form a group known as phospholipids. Two distinct moieties can be differentiated in these four classes of lipids: a hydrophobic moiety and a polar headgroup of hydrophillic substituent (Figures 1 and 2). The length of this polar headgroup varies between the different lipids from a single hydroxyl group in a molecule of cholesterol to a glycoprotein with an M_r of several thousands in the glycophospholipids that serve as protein anchors to the membrane. Triglycerides, which had not been thought to be membrane components and which do not have a polar headgroup, have also been detected in highly purified plasma membranes. Interestingly, these neutral lipids make up about 6% of the lipid content of plasma membranes from malignant cells.⁵

B. Glycerophospholipids

Glycerophospholipids are the most ubiquitous and abundant group of membrane lipids.^6-8 They contain as a common structural backbone a diacylglycerol with a phosphate esterified to the primary hydroxyl group of the sn-glycerol moiety (Figure 1).⁹ With the exception of phosphatidic acid, this phosphate forms a phosphodiester bond with the hydroxyl group of a polar headgroup substituent. The most abundant substituents in eukaryotic cell membranes are choline, ehtanolamine, serine, glycerol, and myo-inositol (Fi...

Table of contents

• Cover
• Title
• Copyright
• Dedication
• Contents
• Chapter 1 Lipid Components of Cellular Membranes
• Chapter 2 Phospholipid Composition of Cellular Membranes
• Chapter 3 Phospholipid Organization in Cellular Membranes
• Chapter 4 Asymmetry in Membrane Phospholipids
• Chapter 5 Role of Phosphatidylinositol in Protein Attachment
• Chapter 6 Phospholipid Metabolism and Turnover: Phosphatidic Acid, Phosphatidylcholine and Phosphatidylethanolamine
• Chapter 7 Inositol Phosphatides and Transmembrane Signaling
• Chapter 8 Role of Glycosyl-Phosphatidylinositols in Insulin Signaling
• Chapter 9 Sphingolipids in Cellular Signaling
• Chapter 10 Biological Actions of the Ether-Linked Glycerophospholipid Platelet Activating Factor
• Index