Classification and Structures of Lipids

Fatty acids and acylglycerols. Fatty acids are carboxylic acids with a long hydrocarbon chain and a varying degree of unsaturation. They are designated by a special notation that includes the number of carbons, followed by a number that indicates the degree of unsaturation. For example, octadecenoic (oleic) acid (1) is denoted as 18 1 and hexadecanoic acid (2) as 16 0. 

Fundamentals of Contemporary Mass Spectrometry, by Chhabil Dass Copyright 2007 John Wiley Sons, Inc. 

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In addition to a classification-based retrieval of lipids, users can search LMSD using either text-based or structure-based search options. The text-based search implementation supports data retrieval by any combination of these data fields Lipid MAPS ID, systematic or common name, mass, formula, category, main class, and subclass data fields. The structure-based search, in conjunction with optional data fields, provides the capability to perform a substmcture search or exact match for the structure drawn by the user. Search results, in addition to structure and annotations, also include relevant links to external databases. 

Edible oils and fats come under the biochemical classification of lipids owing to their insolubility in water. They are composed of two chemically bonded components, a fatty acid and glycerol there are many different fatty acids. When fats and oils are digested in the body, the fatty acids are liberated. Fatty acids are vital in the diet to act as starting materials for cell structures, for other important bodily chemicals including hormones and as an energy source. 

There is a large number of naturally occurring lipids but not all are available commercially. The Lipid Library is a useful source of general information on most classes of lipids, fatty acids and eicosanoids. In addition to this, a more specific database, the Lipid Metabolites and Pathways Strategy (LipidMAPS), provides a classification system for all known lipids and gives information on the structures of these lipids. 

A lipid is an organic substance found in living systems that has limited solubility in water but is soluble in organic solvents. Because their classification is based on insolubility in water rather than on a structural feature such as a functional group, lipids vary widely in their structure and, unlike proteins and polysaccharides, are not polymers. Lipids include fats, oils, steroids, and waxes. The predominant lipids are fats and oils, which make up 95% of the lipids in our diet. The other 5% are steroids and several other lipids that are important to ceU function. 

Two other structures, which together with the lamellar phase are the most important liquid-crystalline phases in lipid-water systems, are shown in Fig. 8.9. It should be pointed out that the classification of lipids into polar and non-polar is best defined from their interaction with water. Lipids which do not give lipid-water phases are thus non-polar whereas those forming aqueous phases are classified as polar lipids. 

The most important and typical enzymes that function at lipid-water interfaces in micelles, liposomes, emulsions, etc., are lipases. Lipases are carboxylic ester hydrolases and have been termed glycerol ester hydrolases (EC3.1.1.3) in the international system of classification. They differ greatly as regards both their origins (bacterial, fungal, plant, mammalian, etc.) and their properties, and they can catalyze the synthesis as well as the hydrolysis of a wide range of different carboxylic esters. Numerous reports have appeared about the structure and function of pancreatic lipases, because they are ubiquitous in mammalian species and play important roles in dietary fat absorption [29,30]. In this part, I will describe a structural feature and its relation to catalytic mechanism at the interfaces of lipases, particularly pancreatic lipases. 

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