Types of Lipids I

Suaib Luqman

epgp books

 

  1. Objectives

 

  • v To know how many types of lipids exist
  • v What are their significance
  • v How they act in a system
  1. Concept Map

3. Description

 

 

3.1 Types of Lipids I

 

 

According to BLOOR (1960), a German biochemist, lipids can be best understood under three categories namely: Simple, Complex and Derived lipids.

 

Simple Lipids

 

Is a saponifiable lipid also known as storage lipid with two types of components i.e. alcohols with esters of fatty acid.

1.   Fats: Are glycerol with esters of fatty acids. Solid at room temperature due to saturation of carbon atoms.

2. Oils: Are fats in the liquid state at room temperature due to unsaturation of carbon atoms.

3.Waxes: Are high molecular weight monohydric alcohols with esters of fatty acids.

 

i.      True Waxes

ii.      Esters of Cholesterol

iii.      Esters of Vitamin A & D

 

Complex Lipids

 

Also known as conjugated or compound lipids are fatty acids esters with groups in toting up to a fatty acid and an alcohol moeity. Being extensively distributed in animals, bacteria and plants, they are the major component of cell membranes and also found in circulating fluids. Complex lipids can be further sub divided into three main subtypes:

 

1.      Phospholipids: Lipids with a phosphate dreg, one glycerol, or an amino/fatty alcohol, with or without one or two fatty chains (remarkably one inositol group, two phosphates or four fatty chains). They frequently have bases with nitrogen and other substituents. In 1719, Hensing JT first reported the occurrence of phosphorus in brain tissue followed by its extraction with ethanol discovered by Vauquelin (1811). Later on alike substances were isolated from brain in alcohol (hot) which were christened as acide cérébrique, cérébrote, matière blanche, or oleophosphoric acid. Gobley (1850), isolated lecithin (synonymous phosphatidylcholine), a phosphorus-containing lipid from yolk of egg (Greek: lecithos meaning egg yolk) and brain and designate it as lecithin. He also revealed that glycerophosphoric  acid  may  possibly  be  brewed  from  lecithin.  Parallely,  Strecker  (1868) demonstrated the presence of choline in bile. With the assistance of supportive findings, Gobley anticipated lecithin structure including choline, margaric acid, oleic acid, phosphoglyceric acid. The phospholipid chemistry made substantial advancement with Thudichum (1828-1901) who isolated various phospholipid fractions and characterized them by means of their nitrogen/phosphorus ratio. He depicted cephalin (synonymous phosphatidylethanolamine), discrete from lecithin by solubility properties. From cephalin fraction, he also isolated ethanolamine and deemed it as a putrefaction artifact of choline. In the Institute of Physiology and Chemistry in Strasbourg (France), Baumann & Renall (1913) described ethanolamine phospholipids. Sphingomyelin (Greek: sphingein to bind tight,  myelos  means  marrow)  was  also  isolated  and  described  by  Thudichum  along  with  its molecular constituents (fatty acid, sphingosine, choline, phosphoric acid). From the studies of Thudichum, it has been concluded that phospholipids are the chemical soul of all bioplasm and  center of life. By 1927, sphingomyelin, lecithin and cephalin (well-defined phospholipids) had been explained: followed by isolation of phosphatidic acid from cabbage leaves by Chibnall, one acetal phosphatide (synonymous plasmalogen) from beef heart by Feulgen (1939), phosphatidylethanolamine, phosphatidylserine and an inositol phospholipid (components of cephalin) from brain by Folch (1942) and a diphosphoinositide (1949), cardiolipin from brain by Pangborn (1944).

 

All through a protracted instance, phospholipids partition was supported on their solvent solubility. Among his most renowned paper, Folch (1942) subjugated this idiosyncrasy to separate ethanolamine, inositol and serine from brain cephalin. Thannhauser et al. (1936) demonstrated the first appearance and use of a aluminum oxide column followed by the use of silica impregnated paper in chromatography by Marinetti et al. (1956) and the use of TLC by Wagner et al. (1956) for isolation, separation and characterization of phospholipids.

 

There are three categories of phospholipids.

 

 

i.   Glycerophospholipids (synonymous Glycerophosphatides or Phosphoglycerides): a group for the glycerol-containing phospholipids. It implies a few imitative of sn-glycero-3-phosphoric acid that contains at least one O-alk-1′-enyl, O-alkyl, or O-acyl residue affixed to the glycerol moiety with a polar head consist of a nitrogenous base, an inositol unit or a glycerol.

 

a.    Phosphatidic acid: When hydrolyzed yield one equivalent of each of glycerol and phosphoric acid.

     b.   Lecithin: It contains fatty acid, phosphoric acid, glycerol and nitrogenous base choline.

c.  Cephalin: It contains fatty acid, glycerol, phosphoric acid, nitrogenous base ethanolamine (coalmine) or the amino acid serine.

d. Plasmalogens: On hydrolysis, it yields one mole each of aliphatic aldehyde, glycerol, fatty acid, phosphoric acid and nitrogenous base ethanolamine or choline.

ii.  Sphingophospholipids (synonymous Sphingosyl phosphatides or Phosphosphingolipids): a group for the sphingosine-containing phospholipids. It contains a long chain base, glycoside moiety with a phosphorus residue.

a.   Sphingomyelin: It contains fatty acid, phosphoric acid and choline. Glycerol is absent.

iii.  Alkylphosphocholines (phospholipid like molecules): a group for the esters of phosphocholine with long chain aliphatic alcohols opposed in chain length, position and unsaturation of the cis-double bond. Eibl et al., (1992) describes its remarkable biological and therapeutic activities (Prog Exp Tumor Res 1992, 34, 1).

 

2. Glycolipids: Lipids with a glycosidic moiety (carbohydrates such as galactose or glucose), fatty acid, sphingosine. Sometimes one or more phosphate groups are present. The long chain derivatives of sugars restrain most frequently in bacteria and plants a glycerol (a diacylglycerol backbone) and in animals (a ceramide backbone). A phosphorylated polysaccharide-lipid complex or a sterol may also be found. Simple glycolipids are composed of a carbohydrate moiety linked to one fatty acid or fatty alcohol. A wide variety of glycolipids are present in bacteria where specific glycopeptidolipids or lipopolysaccharides are also available. Commensurate with the structure, glycolipids have the following categories:

 

i.    Glycerol based glycolipids: It contains mono or oligosaccharide moiety connected to the glycerol (hydroxyl group), alkylated (or acylated) with one or two fatty acids. They might be uncharged and referred as neutral glycoglycerolipids having a phosphate or a sulfate group. Corresponding to their structure, glycerol based glycolipids can be sub-divided into the following:

 

a. Neutral glycoglycerolipids

b.  Glycophospholipids

c.   Sulfoglycoglycerolipids

 

 

Neutral glycoglycerolipids

 

Most commonly this class contains one or two saccharide units allied glycosidically to diacylglycerol or glycerol, however, neutral glycolipids with three or four sachharide units are also reported. Being essential in algae, bacteria and higher plants, they are positioned in photosynthetic membranes and are also present in minor amount in animals. About 85% of neutral glycoglycerolipids (DGDG and MGDG) are present in photosynthetic membranes of all oxygenic photosynthetic organisms. These glycolipids represent the most abundant lipid class on Earth based on the innate loads of photosynthetic organisms. In Plasmodium falciparum (a protozoan responsible for causing malaria), the discovery of a plastid without galactoglycerolipids heaves the issue of trouncing the galactoglycerolipids during evolution. In a number of plants, galactosyl monoacylglycerol with a variety of galactose moieties has also been uttered. There are two families of Neutral glycoglycerolipids.

 

Monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG)

 

Carter et al. (1956) stated the presence of Glycoglycerolipids in the wheat flour extracts followed by its explicit alliance with tylakoid membranes of chloroplasts reported by Benson et al. (1958) and their accurate structure was explicated by Carter et al. (1961). This stiff alliance is epitomized by the algaecide or herbicide commotion of Galvestine (a MGDG synthase inhibitor).

 

 

Tri and tetragalactosyl diacylglycerols (superior homologues of galactolipids) were recognized later in all plant tissues. Zhan et al. (2003) elucidated the structure of trigalactosyl monolinolenylglycerol (a new glyceroglycolipid) isolated from Premna microphylla, a plant used in Chinese folk medicine. A large amount of linolenic acid (18:3 n-3) and an explicit trienoic acid (16:3 n-3) is present in both MGDG and DGDG. In higher plants, linolenic acid is the lone fatty acid in MGDG and hence these plants are known as ‘18:3 plants’. In angiosperms, 16:3 n-3 is absent and linolenic acid is concerted in both sn 1 and sn 2 positions of both DGDG and MGDG. Contrastingly, lower plants (conifers, ferns, mosses, green algae) and some angiospermic families (Solanaceae, Chenopodiaceae, Brassicaceae) have 16:3 n-3 concerted in the galactolipids at sn 2 position, whereas a short proportion of 18:3 n-3 is acylated at both positions. These type of plants have a structural similarity with cyanobacteria and are referred to as 16:3 plants. In photosynthetic diatoms and red algae, a high proportion of 20:5 n-3 galactolipids have been noted. Numerous fatty acids (n-3) have been dogged in MGDG isolated from a brown alga (Sargassum thunbergii). In most fungi, glycosphingolipids is the main glycolipidsand galactolipids have been found in small amounts. In MGDG, an unusual fatty acid (18:3 n-1, ~25 %) was described from a marine diatom (Skeletonema costatum). They were revealed to be metabolized into aldehydes (short chain), octadienal (8:2 n-4) and octatrienal (8:3 n-1) that could have lethal upshot on zooplankton crustaceans. Heptadienal (7:2 n-3), another aldehyde was also known to be produced from eicosapentaenoic acid of MGDG.

 

Two linolenic acid (18:3 n-3) acyl groups containing MGDG have been depicted in fruits of Rosa canina (rose hips) possessing anti-inflammatory properties (inhibits cell migration) which unswervingly correlates to the anti arthritis activity of rose hip herbal remedies. Other reports revealed anti tumor promoting properties, oxygen forage and virus counteracting activities of galactosyl diglycerides from different sources. In Thailand, DGDG isolated from Clinacanthus leaves demonstrated antiviral activity against herpes simplex virus. MGDG extracted from Sargassum muticum, an invasive brown alga has been revealed to display inhibition of the microbial growth including bacteria and fungi (anti-microfouling activity).

 

Specifics have shown that explicit galactolipids with 16:3 n-3 or 18:4 n-3 in the sn 1 position and 20:5 n-3 or 18:5 n-3 in the sn 2 position is directly involved in cytotoxic reactions induced by Phaeodactylum tricornutum, a marine diatom. It has also been discovered that Arabidopsis chloroplasts enclose an arabidopside illustrated by the existence of 12-oxo-phytodienoic acid, a phytohormone intimately allied to jasmonic acid acylated on glycerol carbon (sn 1), the 16:3 n-3 being acylated at sn 2 position. In MGDG, a 12/10 carbon oxoacids have been noticed in Arabidopsis leaves linked to six carbon aldehydes, alcohols and their esters production which are recognized as volatiles of leaf.

In the leaves of Linum usitatissimum, a novel family of oxylipin named Linolipins containing MGDG has been exposed. Esterified residues (one or two) of divinyl ether-etherolenic acid and parallel oxylipin comprising DGDG have also been alienated from the flax leaves damaged by freezing-thawing or inoculated with phytopathogenic bacteria.

 

In Petunia hybrid flower, it has been observed that DGDG synthesis increases and the pistils-

 

pollinic tubes include elevated quantity than any other floral organs. In bacteria, sn 3-O glycosyldiacylglycerols possess glycoside moiety: a-D-mannopyranosyl (1->3)-O-D- mannopyranoside (Micrococcus), a-D-galactopyranosyl (1->2)-O-a-D-glucopyranoside (Lactobacillus), a-D-glucopyranoside (Pneumococcus, Staphylococcus), a-D-glucopyranosyl (1- >2)-O-a-D-glucopyranoside and b-D-galactofuranoside (Mycoplasma), b-D-glucopyranosyl (1- >6)-O-b-D-glucopyranoside (gentobiosyldiacylglycerol, Staphylococcus). In Propionibacterium propionicum, a novel glycoglycerolipid (a-D-glucopyranoside (1->3) a-D-glucopyranoside) enclosing an ether-linked alkyl chain at C-3 position of glycerol has been illustrated. Manca et al. (1992), isolated a diglucosyl diglyceride with an incredibly exceptional diglucosyl structure (1->4) from Thermotoga maritima.

Inquisitively, two moles of palmitic acid esterifies the glycerol moiety and acylated on the 6-OH of the terminal glucose by one molecule of decanoic acid. It has been well-known that the glycolipids present in flour act as surfactants and affect the texture, staling and volume of bread. Selmair et al. (2008, 2010) reviewed the role of glycolipids in breadmaking and have shown that monoalactosylglyceride and its lyso derivative perk up the baking performance of wheat flour. Hamberg (1998) reported DGDG mono estolides in the kernels of oat.

 

  1. Summary

 

In this lecture we learnt about:

 

  • The Types of Lipids (Simple & Complex)
  • Importance of Phospholipids and Glycolipids

 

you can view video onTypes of Lipids I

Weblinks

 

 

Books

 

  1. Biochemistry by Berg JM, Tymoczko JL, Stryer L. 2002. 5th edition. New York: W H Freeman; 2002. http://www.ncbi.nlm.nih.gov/books/NBK22361/
  2. Biochemistry by Thomas Briggs, ‎Albert M. Chandler. 1995. https://books.google.co.in/books?isbn=0387943986
  3. Teaching Innovations in Lipid Science by Randall J. Weselake. 2007. Pages-216 https://books.google.co.in/books?isbn=1420012800

 

 

Journals

 

  1. Deuel HJ. Lipid metabolism. Calif Med. 1950 Apr; 72 (4): 197-200.
  2. Hartroft WS. Effects of various types of lipids in experimental hypolipotropic diets. Fed Proc. 1955 Jun; 14 (2): 655-660.