Hydroxy fatty acid polymer

The Role of Cutin, the Plant Cuticular Hydroxy Fatty Acid Polymer, in the Fungal Interaction with Plants... 

In many organisms the outer envelope or covering consists of polymers of carbohydrate or amino acids. In plants, however, the covering (cuticle) consists of an hydroxy fatty acid polymer called cutin. The underground parts and healed wound surfaces of plants are covered with an analogous material, suberin. Both cutin and suberin are embedded in or associated with a complex mixture of lipids which are termed wax (Section 2.10). 

Plants are unique in that the structural component of their outer envelope (cuticle) consists of a hydroxy fatty acid polymer, cutin, whereas other organisms use polymers of amino acids or carbohydrates for this purpose. Underground parts and healed wound surfaces of plants are protected by another type of lipid-derived polymeric material, suberin, which is laid down outside the plasma membrane and in close contact with the inside of the cell... 

Croteau R, Kolattukudy P E 1975 Biosynthesis of hydroxy fatty acid polymers. Enzymatic epox-idation of 18-hydroxy oleic acid to 18-hydroxy-cis-9,10-epoxystearic acid by a particulate preparation from spinach Spinacia oleracea). Arch Biochem Biophys 170 61-72... 

Stems and leaves of plants are covered with a layer of fatty material. The structural component is an hydroxy fatty acid polymer-cutin. Underground parts and wound surfaces are covered in another type of lipid-derived polymeric material - suberin. Both these polymers are associated with or embedded in a complex mixture of lipids imprecisely called waxes. (Strictly speaking a wax is an ester between a long chain fatty acid and a fatty alcohol section 4.7.)... 

Water repellant To impart water-resistant properties, particularly in greases Aliphatic amines, hydroxy fatty acids and some organic silicone polymers... 

As a general mechanism, the degradation of PVA starts outside the cells via enzymatic attack on the polymer. The resulting products are a mixture of acetoxy hydroxy and hydroxy fatty acids. Upon intracellular enzymatic deacetylation, hydroxy fatty acids are generated that can be further metabolised via the classical p-oxidation pathway and TCA cycle. 

Waxes, in particular cutin and suberin, are polymerized and cross linked structures of hydroxy fatty acids that are resistant to oxidation and to microbial and enzymatic attack. Cutin is found on the outer surface of plant tissue while suberin is mainly associated with roots and bark of plants. Both contain an even number of carbons in the range from C, to C,(,. Cutan and suberan are also highly aliphatic polymers lacking ester cross linkages. They are linked by carbohydrate structures to form glycolipids that are integral parts of microbial cell walls (De Leeuw and Largeau, 1993). 

Other lipids. Waxes are major lipids in a few organisms (e.g., jojoba, sperm whale). Cutins (condensation polymers of hydroxy fatty acids) are discussed in a later chapter (Kolattukudy et el.. Chap. 10). Hydrocarbons other than isopentenoid compounds occur in a variety of species. 

It was generally assumed that oxidation products from oils and fats are poorly absorbed. Indeed, animals can be resistant to the effects of abused oils in their diet (29,30). Nevertheless, orally administered oxidized C-linoleic acid was incorporated into chylomicrons and very low density lipoprotein (VLDL) particles in rats. The absorbed oxidation products were subsequently identified as hydroxy fatty acids (31). Interestingly, dietary glutathione (GSH) reduced the absorption of peroxidized linoleate (32), presumably due to the activity of selenium-dependrait GSH peroxidase present in the intestinal epithelial cell (33). However, these absorption studies used free fatty adds, not triglycerides thus, they cannot address the role of pancreatic lipase and phospholipase. The fate of polymerized fatty adds has not been studied specifically. Whether the intestinal flora could degrade fliese polymers and hence allow their absorption remains to be seen. What is clear is that very little is known about the absorption of oxidized fat in animals and even less in humans. 

Most of the mcl-PHA production strains - with the exception of Pseudomonas putida GPol - accumulate alkanoic mcl-PHA also from unrelated carbon substrates through the fatty acid de novo synthesis pathway. Consequently, glucose may result in polymers containing (R)-3-hydroxy fatty acids with even carbon numbers, e.g., (R)-3-hydroxydecanoate, (R)-3-hydroxyoctanoate, (R)-3-hydroxyhexanoate,... 

The other hpid polymer, suberin, is a heteropolymer, consisting of an aliphatic polyester associated with cross-linked polyaromatics and embedded waxes. Upon transesterification of suberin, the monomers released include C16-C28 m-hydroxy fatty acids and C16-C26 ct, -dicarboxyhc acids, the latter of which are diagnostic monomers, unsubstituted very-long-chain fatty acids (VLCFAs C>i8) and alcohols, glycerol and ferulate. Usually the major components of suberin are -hydroxy derivatives of palmitic and/or oleic acids, but in some cases oo-hydroxy C220 also is a dominant component [37]. Dicarboxylic FAs derived from further oxidation of the -hydroxy-FAs are also found in suberin. 

PHA polymers are thermoplastics that are soluble in halogenated solvents such as chloroform and dichloromethane. Depending on their chemical composition (homo- or copolymer, the hydroxy fatty acids contained), they differ in their physical properties, eg, ductility and elasticity. PHA can be processed on conventional processing equipment. The processability as well as some mechanical properties like impact strength and flexibility can improve when a monomer/comonomer with longer aliphatic chain is used in polymerisation. One of the commercially available types of PHA is polyhy-droxybutyrate (PHB). PHB is similar to polypropylene in some characteristics like melting temperature, tensile strength, moismre resistance, and odour barrier properties (Pouton and Akhtar, 1996). 

Plant epidermal cells are protected by a suberized or waxy cuticle. An additional layer of epicuticu-lar waxes is deposited above the cuticle in many plants. The waxy cuticle consists of cutin. This is a complex, high molecular weight polyester which is readily solubilized in alkali. The structural units of the polymer are hydroxy fatty acids. The latter are similar in structure to the compounds given in 3.7.2.4.I. A segment of the postulated structure of cutin is presented in Fig. 3.16. 

Very recently, lactones have received increasing attention as potential renewable platform chemicals. Perhaps the most prominent bio-based hydroxy fatty acids lactic acid, whose cyclic ester of two lactate molecules serves precursor for the synthesis of bio-based polymers. Fermentative production of hydroxyl-carboxylic acids from agro-industrial waste is an alternative to the synthesis from dwindling fossil resources (Fiichtenbusch et al. 2000). The enzymatic machinery for the production of polyhydroxyalkanoates (PHA) in bacteria offers catalytic pathways for the production of these lactone precursors (Efe et al. 2008). Recent examples include the microbial synthesis of y-butyrolactone and y-valerolactone. Particularly y-valerolactone is of importance and ranks among the top key components of the biomass-based economy. Microbial processes thus offer the perspective of a sustainable fermentative production of optically pure renewable lactones. 

Plants were probably the first to have polyester outerwear, as the aerial parts of higher plants are covered with a cuticle whose structural component is a polyester called cutin. Even plants that live under water in the oceans, such as Zoestra marina, are covered with cutin. This lipid-derived polyester covering is unique to plants, as animals use carbohydrate or protein polymers as their outer covering. Cutin, the insoluble cuticular polymer of plants, is composed of inter-esterified hydroxy and hydroxy epoxy fatty acids derived from the common cellular fatty acids and is attached to the outer epidermal layer of cells by a pectinaceous layer (Fig. 1). The insoluble polymer is embedded in a complex mixture of soluble lipids collectively called waxes [1], Electron microscopic examination of the cuticle usually shows an amorphous appearance but in some plants the cuticle has a lamellar appearance (Fig. 2). 

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