FabA enzyme

E. coli possesses two p-hydroxyacyl-ACP dehydratases. One is encoded by fabZ, and is active on all chain lengths of saturated and unsaturated intermediates. This enzyme is distinct from the dual-function P-hydroxydecanoyl-ACP dehydratase/isomerase (encoded by fabA) first described by Bloch and coworkers. The FabA enzyme dehydrates saturated, but not unsaturated, fatty acid intermediates and catalyzes a key isomerization reaction at the point where the biosynthesis of unsaturated fatty acids diverges from saturated fatty... 

Chloroplast GDH enzymes have been characterized, for example, from Viciafaba (Leech and Kirk, 1968) and lettuce (Lea and Thurman, 1972). The V. faba enzyme had higher activity with NADPH than with NADH, though quantitative estimates of activity ratios were complicated by the contamination of chloroplast fractions by mitochondria. The NADH/NADPH activity ratio of the lettuce chloroplast enzyme was observed to be 1 1. 

LONGSTAFF M, MCNAB J M (1991) The inhibitory effects of hull polysaccharides and tannins of field beans (Vida faba L.) on the digestion of amino acids, starch and hpid and on digestive enzyme activities in young chicks. Br. TNutr. 65 199-216. 

Polyphenol oxidase occurs within certain mammalian tissues as well as both lower (46,47) and higher (48-55) plants. In mammalian systems, the enzyme as tyrosinase (56) plays a significant role in melanin synthesis. The PPO complex of higher plants consists of a cresolase, a cate-cholase and a laccase. These copper metalloproteins catalyze the one and two electron oxidations of phenols to quinones at the expense of 02. Polyphenol oxidase also occurs in certain fungi where it is involved in the metabolism of certain tree-synthesized phenolic compounds that have been implicated in disease resistance, wound healing, and anti-nutrative modification of plant proteins to discourage herbivory (53,55). This protocol presents the Triton X-114-mediated solubilization of Vida faba chloroplast polyphenol oxidase as performed by Hutcheson and Buchanan (57). 

Galactinol (15) is known to serve as a D-galactosyl donor in D-galac-tosylation reactions catalyzed by specific enzymes. Kandler and coworkers293 showed that the enzyme preparations from the mature seeds of V. faba and wheat germ catalyze the synthesis of raffinose from galactinol and sucrose. The reaction does not take place if galac-... 

This would, however, require the addition of myo-inositol to the reaction mixture, unless this compound should already be present in a bound form in the enzyme preparation. The preparations from V.faba, G. max,910 and the chloroplasts of P. sativum888 were all thoroughly dialyzed, and no myo-inositol was added in the assay. Thus, this controversy requires further investigation. The maturity and the physiological state of the seeds are important factors in detecting a given enzyme, and consequently, these factors should be taken into consideration in future investigations. 

Kandler and coworkers818 isolated from the mature seeds of V.faba (see also, Refs. 293 and 298) an enzyme that transfers the D-galactosyl group of galactinol to raffinose, yielding stachyose (compare with Refs. 34, 296, and 615), and to stachyose, yielding verbascose. When... 

Castanon, J.I.R. and Marquardt, R.R. (1989) Effect of enzyme addition, autoclave treatment and fermenting on the nutritive value of field beans (Vicia faba L.). Animal Feed Science and Technology 26, 71-79. 

Several cDNA clones encoding two different ADPGlc PPase polypeptides have been isolated from a cotyledonary library of V faba L.125 Sequences of the cDNAs were closely related to the ADPGlc PPase small subunit of other plants. One polypeptide is expressed in developing cotyledons and leaves, while the other is found solely in cotyledons. Crude extracts were assayed for ADPGlc PPase activity, and it was found that the enzyme from cotyledons is not activated by 3PGA, whereas the leaf enzyme was activated more than 5-fold. Pi inhibited both enzymes. These experiments were performed in the pyrophos-phorolysis direction. Whether 3PGA could reverse Pi inhibition was not studied.125... 

ATPase activity was also studied by Friebe et al. in 1997.17 They correlated the BOA and DIBOA effects on radicle elongation of Avena sativa seedlings with their effects on the activity of plasma membrane H+-ATPase from roots of Avena sativa cv. Jumbo and from Vida faba cv. Alfred. They hypothesized that an alteration in the plasma membrane ATPase activity could be the reason for an abnormal nutrient absorption in plants exposed to hydroxamic acids, because of the role that this enzyme plays in the ion gradient and, therefore, in the ionic transport through plasma membrane. The results of this experiment showed a strong inhibition in the activity of this enzyme in the plasma membrane of chloroplast and mitochondria when it was exposed to BOA and DIMBOA. This alteration implies early interactions with the assayed hydroxamic acids. 

Ross, H.A., McRae, D., and Davies, H.V, 1996, Sucrolytic enzyme activities in cotyledons of the faba bean (developmental changes and purification of alkaline invertase). Plant Physiol. 111(1) 329-338. 

The enhanced chemiluminescense obtained with the horseradish peroxidase-H202-luminol (139) system was applied to the development of a CLD biosensor for p-iodophenol, coumaric acid (26), 2-naphthol and hydrogen peroxide. The enzyme was immobilized by microencapsulation in a sol-gel matrix. LOD for the phenolic compounds were 0.83 p,M, 15 nM and 48 nM, respectively. A remote version of the enhanced biosensor was designed by directly immobilizing the enzyme on the tip of an optical fiber. This model was used for H2O2 assay. LOD was 52.2 p,M, with RSD 4.7% (w = 4) °. A bioluminescent response was obtained for phenols with pA a > 7 in the presence of a recombinant Escherichia coli strain, DPD2540, containing a fabA luxCDABE fusion this behavior may have analytical applications. 

In E. coli, UFAs are generated through the activity of FabA, which anaerobically introduces the double bond into a 10-carbon intermediate formed in the fatty acid biosynthetic pathway (Bloch, 1963, for a recent review see Mansilla et al., 2004). However, other bacteria lacking fab A synthesize UFAs under anoxic conditions. For example, Streptococcus pneumoniae compensates FabA absence with an enzyme called FabM, that is capable of isomerising the trans unsaturated bond of the key 10-carbon intermediate to its cA-isomer (Marrakchi et al., 2002). Nevertheless, FabM seems to be specific for streptococci indicating that there are new anaerobic pathways of UFAs synthesis to be discovered. 

Four enzymes participate in each iterative cycle of chain elongation (Fig. 3). The acetoacyl-ACP formed from the initiating FabH condensation is reduced by an NADPH-dependent P-ketoacyl-ACP reductase (fabG), and a water molecule is then removed by a P-hydroxyacyl-ACP dehydrase (fabA otfabZ). The last step is catalyzed by enoyl-ACP reductase (fabl or fabK) to form a saturated acyl-ACP, which serves as the substrate for another condensation reaction or when the chain length reaches 16-18 carbons is utilized for membrane phospholipid synthesis. p-Ketoacyl-ACP synthase I or II (fabB or fabF) initiates additional... 

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