Type of fat derived from glycerol and two fatty acids
General chemical structures of 1,2-diacylglycerols (top) and 1,3-diacylglycerols (bottom), where R1 and R2 are fatty acid side chains
A diglyceride, or diacylglycerol (DAG), is a
glyceride consisting of two
fatty acid chains
covalently bonded to a
glycerol molecule through
ester linkages.[1] Two possible forms exist, 1,2-diacylglycerols and 1,3-diacylglycerols. Diglycerides are natural components of food fats, though minor in comparison to
triglycerides.[2] DAGs can act as
surfactants and are commonly used as
emulsifiers in processed foods.
DAG-enriched oil (particularly 1,3-DAG) has been investigated extensively as a
fat substitute due to its ability to suppress the accumulation of body fat;[3][4] with total annual sales of approximately USD 200 million in Japan since its introduction in the late 1990s till 2009.[3]
Production
Diglycerides are a minor component of many
seed oils and are normally present at ~1–6%; or in the case of
cottonseed oil as much as 10%.[5] Industrial production is primarily achieved by a
glycerolysis reaction between
triglycerides and glycerol. The raw materials for this may be either
vegetable oils or
animal fats.[6]
Food additive
Diglycerides, generally in a mix with
monoglycerides (
E471), are common food additives largely used as
emulsifiers. The values given in the nutritional labels for total fat, saturated fat, and trans fat do not include those present in mono- and diglycerides.[citation needed] They often are included in bakery products, beverages,
ice cream,
peanut butter,
chewing gum,
shortening, whipped toppings,
margarine, confections, and some snack products, such as
Pringles.
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.[7]
Other
In addition to activating PKC, diacylglycerol has a number of other functions in the
cell:
Synthesis of diacylglycerol begins with
glycerol-3-phosphate, which is derived primarily from
dihydroxyacetone phosphate, a product of
glycolysis (usually in the cytoplasm of liver or adipose tissue cells). Glycerol-3-phosphate is first
acylated with acyl-coenzyme A (acyl-CoA) to form
lysophosphatidic acid, which is then acylated with another molecule of acyl-CoA to yield
phosphatidic acid. Phosphatidic acid is then de-phosphorylated to form diacylglycerol.
Dietary fat is mainly composed of
triglycerides. Because triglycerides cannot be absorbed by the digestive system, triglycerides must first be enzymatically digested into
monoacylglycerol, diacylglycerol, or free fatty acids. Diacylglycerol is a precursor to
triacylglycerol (triglyceride), which is formed in the addition of a third fatty acid to the diacylglycerol under the catalysis of
diglyceride acyltransferase.
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.[8]
Activation of
PKC-θ by diacylglycerol may cause
insulin resistance in muscle by decreasing
IRS1-associated
PI3K activity.[9] Similarly, activation of
PKCε by diacyglycerol may cause insulin resistance in the liver.[9][10]
^Sonntag, Norman O. V. (1982). "Glycerolysis of fats and methyl esters — Status, review and critique". Journal of the American Oil Chemists' Society. 59 (10): 795A–802A.
doi:
10.1007/BF02634442.
ISSN0003-021X.
S2CID84808531.