Chain shortening, fatty acids

STEP 4 The bond between C2 and C3 is broltcti by nodrophiltc attadc ofcoenzynic Aon the C3 carbonyl group in a rctroAaiscti reaction to yield acetyl CoA and a chain shortened fatty acid. 

The concept of a peroxisome being a closed compartiment also requires transport systems for fatty acids which undergo oxidation in the peroxisome. Since oxidation of fatty acids in peroxisomes is incomplete, the peroxisome must also have systems to allow export of chain-shortened fatty acids. Recent evidence notably in yeast suggests that... 

Changes in reductase activity could result in altered pheromone amounts. The lightbrown apple moth, Epiphyas postvittana, exhibits a decline in pheromone titers with age that is not due to reduced PBAN levels (Foster and Roelofs, 1994). To determine what is responsible for the decline in titers, different deuterium-labeled precursors were applied to the glands of different aged females. Biosynthesis of the major pheromone component, Ell-14 OAc, occurs by chain shortening 16 acid to 14 acid followed by Ell desaturation, reduction, and acetylation (Foster and Roelofs, 1990). Application of deuterium-labeled intermediates indicated that the senescent decline in pheromone titers was due to the reduction in fatty acid reductase activity (Foster and Greenwood, 1997). It is unknown if a decline in reductase enzyme activity is also responsible for observed senescent decline in pheromone titers of other female moths (Foster and Greenwood, 1997). 

Polymorphic Tendency of the Major Solid Triacylglycerols (TAG) in Vegetable Margarines and Shortenings of 16 and 18 Carbon Chain-Length Fatty Acids ... 

Were the short chains made by stopping the synthesis at an earlier stage, or were the longer chains of fatty acids shortened ... 

The four steps of the /3-oxidation pathway, resulting in the cleavage of an acetyl group from the end of the fatty-acid chain. The key chain-shortening step is a retro-Claisen reaction of a /3-keto thioester. Individual steps are explained in the text. 

The carbon chains of samrated fatty acids form a zigzag pattern when extended, as at low temperamres. At higher temperatures, some bonds rotate, causing chain shortening, which explains why biomembranes become thinner with increases in temperamre. A type of geometric isomerism occurs in unsaturated fatty acids, depending on the orientation of atoms or groups around the axes of double bonds, which do not allow rotation. If the acyl chains are on the same side of the bond, it is cis-, as in oleic acid if on opposite sides, it is tram-, as in elaidic acid, the tram isomer of oleic acid (Fig-... 

The enzymes in peroxisomes do not attack shorter-chain fatty acids the P-oxidation sequence ends at oc-tanoyl-CoA. Octanoyl and acetyl groups are both further oxidized in mitochondria. Another role of peroxisomal P-oxidation is to shorten the side chain of cholesterol in bile acid formation (Chapter 26). Peroxisomes also take part in the synthesis of ether glycerolipids (Chapter 24), cholesterol, and dolichol (Figure 26-2). 

Fatty acids are often described by numbers such as 16 0, 18 1 or 18 3. The first number (16 or 18) is used to describe the number of carbon atoms in the chain whilst the second (0,1,3) gives the number of C=C double bonds in the molecule. Palmitic acid can therefore be shortened to 16 0 whilst oleic acid is 18 1... 

Fig.i General biosynthetic pathways for the production of alcohol, aldehyde, and acetate ester pheromone components in female moths. Top production of saturated fatty acids. Middle production of monounsaturated fatty acids and limited chain shortening produces intermediate compounds that can be reduced to an alcohol. Aldehyde and acetate ester pheromones are produced by an oxidase and acetyl-transferase, respectively. Bottom biosynthetic pathway for the production of the acetate ester pheromone components in the cabbage looper moth, Trichoplusia ni. The CoA derivatives are reduced and acetylated to form the acetate esters. Additional pheromone components include 12 OAc and ll-12 OAc... 

Macrolide aggregation pheromones produced by male cucujid beetles are derived from fatty acids. Feeding experiments with labeled oleic, linoleic, and palmitic acids indicate incorporation into the macrolide pheromone component [ 117 ]. The biosynthesis of another group of beetle pheromones, the lactones, involves fatty acid biosynthetic pathways. Japonilure and buibuilactone biosynthesized by the female scarab, Anomalajaponica, involves A9 desaturation of 16 and 18 carbon fatty acids to produce Z9-16 CoA and Z9-18 CoA,hydroxylation at carbon 8 followed by two rounds of limited chain shortening and cyclization to the lactone [118]. The hydroxylation step appears to be stereospecific [118]. 

Summary Thalassemias as a group are the most common genetic diseases in the world. Beta thalassemia is an inherited blood disorder in which the body produces an abnormal form of hemoglobin. The disorder results in excessive destruction of red blood cells, which in a severe form manifests as life-shortening anemia shortly after birth. Short-chain fatty acids had previously been shown to be useful in the... 

In contrast to pheromones that involve single complex compounds, many moth species have been found to utilize a specific blend of relatively simple fatty acid-derived compounds. It appears that the evolution of a unique enzyme, A1 desaturase, used in combination with 2-carbon chain-shortening reactions (Figure 3) has allowed moth species to produce a variety of unsaturated acetates, aldehydes, and alcohols that can be combined in almost unlimited blends to impart species specificity. For example, biosynthetic precursors for the six-component pheromone blend of acetates for the cabbage looper moth (12) (Figure 2) can be determined easily from the cascade of acyl intermediates produced by the A11-desaturase and chain-shortening reactions (Figure 3). 

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