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A di-glyceride, or a diacyl-glycerol (DAG), is a glyceride consisting of two fatty acid chains covalently bonded to a glycerol molecule through ester linkages. One example, shown on the right, is 1-palmitoyl-2-oleoyl-glycerol, which contains side-chains derived from palmitic acid and oleic acid. Diacylglycerols can also have many different combinations of fatty acids attached at both the C-1 and C-2 positions.
Mono- and diglycerides (E471) are common food additives used to blend together certain ingredients, such as oil and water, which would not otherwise blend well. The values given in the nutritional labels for total fat, saturated fat, and trans fat do not include those present in mono- and diglycerides.
The commercial source may be either animal (cow- or hog-derived) or vegetable, derived primarily from partially hydrogenated soy bean and canola oil. They may also be synthetically produced. They are often found in bakery products, beverages, ice cream, peanut butter, chewing gum, shortening, whipped toppings, margarine, confections, and candies.
In biochemical signaling, diacylglycerol functions as a second messenger signaling lipid, and is a product of the hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) by the enzyme phospholipase C (PLC) (a membrane-bound enzyme) that, through the same reaction, produces inositol trisphosphate (IP3). Although inositol trisphosphate diffuses into the cytosol, diacylglycerol remains within the plasma membrane, due to its hydrophobic properties. IP3 stimulates the release of calcium ions from the smooth endoplasmic reticulum, whereas DAG is a physiological activator of protein kinase C (PKC). The production of DAG in the membrane facilitates translocation of PKC from the cytosol to the plasma membrane.
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.
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.