Fatty acids acetate, role

Problem 29.5 Evidence for the role of acetate in fatty-acid biosynthesis comes from isotope-labeling experiments. If acetate labeled with 13C in the methyl group ( CFtyCC H) were incorporated into fatty acids, at what positions in the fatty-acid chain would you expect the, 3C label to appear ... 

When cells are grown on non-aliphatic substrates, such as glucose, fructose, acetate, or glycerol, these are converted to appropriate precursors that can be incorporated into poly(3HAMCL)s via fatty acid synthesis. The resulting PHAs have a monomer composition that is similar to that seen after growth on alkanes, often with 3-hydroxydecanoic acid as the major monomer. ( -Oxidation does not seem to play a role in the conversion of these substrates into poly(3HAMCL) since the addition of a -oxidation inhibitor did not affect the monomer composition [47]. 

Attractive Compounds. The female-produced sex pheromone of the yellow mealworm beetle, Tenebrio molitor, is (R)-4-methyl- 1-nonanol [316] 163 (Scheme 18). Careful investigations on the biosynthesis of this compound [317] revealed that it is produced through a modification of normal fatty acid biosynthesis (Fig. 1, Fig. 2) propanoate serves as the starter, while formal chain elongation with acetate, propanoate, and acetate (accompanied by removal of the oxygens) produces 4-methylnonanoate which yields the pheromone alcohol after reduction. The structures and role of proteins that are present in the hemolymph or secreted by the tubular accessory glands of T. molitor, and that may carry lipophilic chemical messengers (like pheromones) are under investigation [318,319]. 

Esterases play a role in regulating the platelet-activating factor (PAF), a lipid with hypotensive properties [96], Phospholipase A2 (EC 3.1.1.4) is involved in this pathway by hydrolyzing a precursor to lyso-PAF and a free fatty acid. The activity of PAF, formed by acetylation of lyso-PAF, is controlled by an esterase hydrolyzing the acetate moiety [100]. 

This is a complex molecule, made up of an adenine nucleotide (ADP-3 -phosphate), pantothenic acid (vitamin B5), and cysteamine (2-mercaptoethylamine), but for mechanism purposes can be thought of as a simple thiol, HSCoA. Pre-eminent amongst the biochemical thioesters is the thioester of acetic acid, acetyl-coenzyme A (acetyl-CoA). This compound plays a key role in the biosynthesis and metabolism of fatty acids (see Sections 15.4 and 15.5), as well as being a building block for the biosynthesis of a wide range of natural products, such as phenols and macrolide antibiotics (see Box 10.4). 

S ATP -P acetate <1-18> (<8> acetate kinase/phosphotransacetylase, major role of this two-enzyme sequence is to provide acetyl coenzyme A which may participate in fatty acid synthesis, citrate formation and subsequent oxidation [1] <3> function in the metabolism of pyruvate or synthesis of acetyl-CoA coupling with phosphoacetyltransacetylase [15] <11> function in the initial activation of acetate for conversion to methane and CO2 [19] <10> key enzyme and responsible for dephosphorylation of acetyl phosphate with the concomitant production of acetate and ATP [30]) (Reversibility r <1-18> [1, 2, 5-21, 24-27, 29-33]) [1, 2, 5-21, 24-27, 29-33]... 

Chromium also slimulales fatty acid and cholesterol synthesis from acetate in liver. Thai chromium is an essential cofaclor for the action of insulin on the rat lens was shown by Parkas in 1964. In the absence of the element, no significant insulin effect on glucose utilization of lens can be demonstrated. Chromium supplementation to the donor animals resulls in a significant response of lens tissue to the hormone. Numerous other findings indicate that chromium may play several vital roles in biological systems. 

In insects, especially Diptera, several pioneer studies reviewed by Blomquist et al. (1987) established that long chain hydrocarbons, some of which play a pheromone role, were derived from very long chain fatty acids by reduction and decarboxylation. Thus, pheromone biosynthesis shares steps with those leading to basic lipid molecules and also with those of the well-known pheromones of Lepidoptera (Roelofs and Wolf, 1988). All often display several double bonds located in various positions while the volatile butterfly compounds bear functional groups (acetate, aldehyde or alcohol) and aliphatic chains with 12-16 carbons. Contact pheromones of flies have much longer chains (21C-39C) (Pennanec h et al., 1991). 

Partial inhibition of glycolysis by saturated fatty acids has been observed in Ehrlich ascites tumor cells. Palmitate and acetate decreased glutamate formation from glutamine (the first step in glutaminolysis) in this cell line, suggesting the possible role of fatty acids as an alternative energy source (Butler et al., 1999). 

Carnitine is required for transport of long-chain fatty adds into mitochondria hence, carnitine plays an essential role in normal oxidative metabolism as well as in the formation of ketone bodies. The concentration of free carnitine in muscle is about 4.0 mmol/kg. The concentration of carnitine boimd to long-chain fatty adds (fatty acyl-camitine) is lower, about 0.2 mmol/kg. Short-chain fatty acids, including acetic, are also esterified to carnitine, but the functions of these complexes are not clear. There is some indication that keto forms of BCAAs (BCKAs) can also be esterified to carnitine. These complexes can then be transported into the mitochondria for complete oxidation of the BCKAs. The importance of this mode of BCKA transport is not clear (Takakura et ah, 1997). 

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