A diglyceride, or diacylglycerol (DAG), is a
glyceride
Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic.
Glycerol has three hydroxyl functional groups, which can be esterified with one, two, or three fatty acids ...
consisting of two
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...
chains
covalently bonded
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
to a
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
molecule through
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...
linkages. Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. DAGs can act as
surfactants
Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsion#Emulsifiers , ...
and are commonly used as
emulsifier
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Altho ...
s in processed foods.
DAG-enriched oil (particularly 1,3-DAG) has been investigated extensively as a
fat substitute A fat substitute is a food product with the same functions, stability, physical, and chemical characteristics as regular fat, with fewer Calories per gram than fat. They are utilized in the production of low fat and low calorie foods.
Background
Fa ...
due to its ability to suppress the accumulation of body fat;
with total annual sales of approximately USD 200 million in Japan since its introduction in the late 1990s till 2009.
Production
Diglycerides are a minor component of many
seed oil
Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fats ...
s and are normally present at ~1–6%; or in the case of
cottonseed oil
Cottonseed oil is cooking oil from the seeds of cotton plants of various species, mainly ''Gossypium hirsutum'' and ''Gossypium herbaceum'', that are grown for cotton fiber, animal feed, and oil.
Cotton seed has a similar structure to other oi ...
as much as 10%. Industrial production is primarily achieved by a
glycerolysis
In organic chemistry glycerolysis refers to any process in which chemical bonds are broken via a reaction with glycerol. The term refers almost exclusively to the transesterification reaction of glycerol with triglycerides (fats/oils) to form mi ...
reaction between
triglycerides
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as we ...
and glycerol. The raw materials for this may be either
vegetable oil
Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fat ...
s or
animal fat
Animal fats and oils are lipids derived from animals: oils are liquid at room temperature, and fats are solid. Chemically, both fats and oils are composed of triglycerides. Although many animal parts and secretions may yield oil, in commercial p ...
s.
Food additive
Diglycerides, generally in a mix with
monoglyceride
Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differen ...
s (
E471
Mono- and diglycerides of fatty acids ( E471) refers to a naturally occurring class of food additive composed of diglycerides and monoglycerides which is used as an emulsifier. It is also used as a fruit coating agent. This mixture is also some ...
), are common food additives largely used as
emulsifiers
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids. Although ...
. The values given in the nutritional labels for total fat, saturated fat, and ''trans'' fat do not include those present in mono- and diglycerides. They often are included in bakery products, beverages,
ice cream
Ice cream is a sweetened frozen food typically eaten as a snack or dessert. It may be made from milk or cream and is flavoured with a sweetener, either sugar or an alternative, and a spice, such as cocoa or vanilla, or with fruit such as str ...
,
peanut butter
Peanut butter is a food paste or spread made from ground, dry-roasted peanuts. It commonly contains additional ingredients that modify the taste or texture, such as salt, sweeteners, or emulsifiers. Peanut butter is consumed in many countri ...
,
chewing gum
Chewing gum is a soft, cohesive substance designed to be chewed without being swallowed. Modern chewing gum is composed of gum base, sweeteners, softeners/plasticizers, flavors, colors, and, typically, a hard or powdered polyol coating. Its te ...
,
shortening
Shortening is any fat that is a solid at room temperature and used to make crumbly pastry and other food products. Although butter is solid at room temperature and is frequently used in making pastry, the term ''shortening'' seldom refers to bu ...
, whipped toppings,
margarine
Margarine (, also , ) is a spread used for flavoring, baking, and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The spread was orig ...
, confections, and some snack products, such as
Pringles
Pringles is an American brand of stackable potato-based crisps. Originally sold by Procter & Gamble (P&G) in 1968 and marketed as "Pringle's Newfangled Potato Chips", the brand was sold in 2012 to the current owner, Kellogg's.
As of 2011, Pri ...
.
Biological functions
Protein kinase C activation
In biochemical signaling, diacylglycerol functions as a
second messenger
Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules—the first messengers. (Intercellular signals, a non-local form or cell signaling, encompassing both first me ...
signaling lipid, and is a product of the
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
of the phospholipid
phosphatidylinositol 4,5-bisphosphate
Phosphatidylinositol 4,5-bisphosphate or PtdIns(4,5)''P''2, also known simply as PIP2 or PI(4,5)P2, is a minor phospholipid component of cell membranes. PtdIns(4,5)''P''2 is enriched at the plasma membrane where it is a substrate for a number of ...
(PIP
2) by the enzyme
phospholipase C
Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role ...
(PLC) (a
membrane
A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...
-bound enzyme) that, through the same reaction, produces
inositol trisphosphate
Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the p ...
(IP
3). Although inositol trisphosphate diffuses into the
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
, diacylglycerol remains within the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
, due to its
hydrophobic
In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, th ...
properties. IP
3 stimulates the release of calcium ions from the smooth
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
, whereas DAG is a physiological activator of
protein kinase C
In cell biology, Protein kinase C, commonly abbreviated to PKC (EC 2.7.11.13), is a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and t ...
(PKC). The production of DAG in the membrane facilitates translocation of PKC from the cytosol to the
plasma membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...
.
Munc13 activation
Diacylglycerol has been shown to exert some of its excitatory actions on vesicle release through interactions with the presynaptic priming protein family
Munc13. Binding of DAG to the C1 domain of Munc13 increases the fusion competence of synaptic vesicles resulting in potentiated release.
Diacylglycerol can be mimicked by the tumor-promoting compounds
phorbol esters
Phorbol esters are a class of chemical compounds found in a variety of plants, particularly in the families Euphorbiaceae and Thymelaeaceae. Chemically, they are ester
In chemistry, an ester is a compound derived from an oxoacid (organic or in ...
.
Other
In addition to activating PKC, diacylglycerol has a number of other functions in the
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
:
* a source for
prostaglandin
The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are derive ...
s
* a precursor of the
endocannabinoid
Cannabinoids () are several structural classes of compounds found in the cannabis plant primarily and most animal organisms (although insects lack such receptors) or as synthetic compounds. The most notable cannabinoid is the phytocannabinoid tet ...
2-arachidonoylglycerol
2-Arachidonoylglycerol (2-AG) is an endocannabinoid, an endogenous agonist of the CB1 receptor and the primary endogenous ligand for the CB2 receptor. It is an ester formed from the omega-6 fatty acid arachidonic acid and glycerol. It is present ...
* an activator of a subfamily of
transient receptor potential canonical (TRPC) cation channels, TRPC3/6/7.
Metabolism
![Glycerol-3-phosphate](https://upload.wikimedia.org/wikipedia/commons/d/d8/Glycerol-3-phosphate.png)
Synthesis of diacylglycerol begins with
glycerol-3-phosphate
''sn''-Glycerol 3-phosphate is the organic ion with the formula HOCH2CH(OH)CH2OPO32-. It is one of three stereoisomers of the ester of dibasic phosphoric acid (HOPO32-) and glycerol. It is a component of glycerophospholipids. Equally appropria ...
, which is derived primarily from
dihydroxyacetone phosphate
Dihydroxyacetone phosphate (DHAP, also glycerone phosphate in older texts) is the anion with the formula HOCH2C(O)CH2OPO32-. This anion is involved in many metabolic pathways, including the Calvin cycle in plants and glycolysis.Nelson, D. L.; ...
, a product of
glycolysis
Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...
(usually in the cytoplasm of liver or adipose tissue cells). Glycerol-3-phosphate is first
acylated
In chemistry, acylation (or alkanoylation) is the chemical reaction in which an acyl group () is added to a compound. The compound providing the acyl group is called the acylating agent.
Because they form a strong electrophile when treated with ...
with acyl-coenzyme A (acyl-CoA) to form
lysophosphatidic acid
Lysophosphatidic acid (LPA) is a phospholipid derivative that can act as a signaling molecule.
Function
LPA acts as a potent mitogen due to its activation of three high-affinity G-protein-coupled receptors called LPAR1, LPAR2, and LPAR3 (also kn ...
, which is then acylated with another molecule of acyl-CoA to yield
phosphatidic acid Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels. Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty ac ...
. Phosphatidic acid is then de-phosphorylated to form diacylglycerol.
Dietary fat is mainly composed of
triglyceride
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
s. Because triglycerides cannot be absorbed by the digestive system, triglycerides must first be enzymatically digested into
monoacylglycerol
Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differen ...
, diacylglycerol, or free fatty acids. Diacylglycerol is a precursor to
triacylglycerol
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as we ...
(triglyceride), which is formed in the addition of a third fatty acid to the diacylglycerol under the catalysis of
diglyceride acyltransferase
Diglyceride acyltransferase (or O-acyltransferase), DGAT, catalyzes the formation of triglycerides from diacylglycerol and fatty acyl-CoA]. The reaction catalyzed by DGAT is considered the terminal and only committed step in triglyceride synth ...
.
Since diacylglycerol is synthesized via phosphatidic acid, it will usually contain a saturated fatty acid at the C-1 position on the glycerol moiety and an unsaturated fatty acid at the C-2 position.
Diacylglycerol can be phosphorylated to phosphatidic acid by
diacylglycerol kinase
Diacylglycerol kinase (DGK or DAGK) is a family of enzymes that catalyzes the conversion of diacylglycerol (DAG) to phosphatidic acid (PA), utilizing ATP as a source of the phosphate. In non-stimulated cells, DGK activity is low, allowing DAG ...
.
Insulin resistance
Activation of
PKC-θ
In cell biology, Protein kinase C, commonly abbreviated to PKC (EC 2.7.11.13), is a family of protein kinase enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and th ...
by diacylglycerol may cause
insulin resistance
Insulin resistance (IR) is a pathological condition in which cell (biology), cells fail to respond normally to the hormone insulin.
Insulin is a hormone that facilitates the transport of glucose from blood into cells, thereby reducing blood gluco ...
in muscle by decreasing
IRS1
Insulin receptor substrate 1 (IRS-1) is a signaling adapter protein that in humans is encoded by the ''IRS-1'' gene. It is a 131 kDa protein with amino acid sequence of 1242 residues. It contains a single pleckstrin homology (PH) domain at the N-te ...
-associated
PI3K
Phosphoinositide 3-kinases (PI3Ks), also called phosphatidylinositol 3-kinases, are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which i ...
activity.
Similarly, activation of
PKCε
Protein kinase C epsilon type (PKCε) is an enzyme that in humans is encoded by the ''PRKCE'' gene. PKCε is an isoform of the large PKC family of protein kinases that play many roles in different tissues. In cardiac muscle cells, PKCε regulate ...
by diacyglycerol may cause insulin resistance in the liver.
See also
*
Lipid
Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...
*
Monoglyceride
Monoglycerides (also: acylglycerols or monoacylglycerols) are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two differen ...
*
Triglyceride
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and ''glyceride'').
Triglycerides are the main constituents of body fat in humans and other vertebrates, as w ...
References
{{Transient receptor potential channel modulators
Lipids
Fatty acid esters
Signal transduction
Food additives
Glycerol esters