Ferulic acid oxidation

The antioxidant property of ferulic acid and related compounds from rice bran was reported by Kikuzaki et al, (2002). Their results indicated that these compounds elicit their antioxidant function through radical scavenging activity and their affinity with lipid substrates. Another recent study reported by Butterfield et al, (2002) demonstrated that ferulic acid offers antioxidant protection against hydroxyl and peroxyl radical oxidation in synaptosomal and neuronal cell culture systems in vitro. The effect of ferulic acid on blood pressure (BP) was investigated in spontaneously hypertensive rats (SHR). After oral administration of ferulic acid the systolic blood pressure (SBP) decreased in a dose-dependent manner. There was a significant correlation between plasma ferulic acid and changes in the SBP of the tail artery, suggesting... 

Takahama, U. Oniki, T. Enhancement of peroxidase-dependent oxidation of sinapyl alcohol hy esters of 4-coumaric and ferulic acid. In Plant Peroxidases, Biochemistry and Physiology Ohinger, C. Burner, U. Ebermann, R. Penel, C. Greppin, H., Eds. Universite de Geneve, Geneve Switzerland, 1996 pp. 118-123. 

Wang et al. (62) reported the oxidative polymerization of a mixture of phenolic compounds in aqueous solution containing mont-morillonlte, illite, and kaolinite, each of which had been mixed with quartz in a 3 7 ratio, and by quartz alone. The mixture of phenolic compounds contained gallic acid, pyrogallol, protocatechuic acid, caffeic acid, orcinol, ferulic acid, p-coumaric acid, syringic acid, vanillic acid, and p-hydroxybenzoic acid. The oxidative... 

The presence of feruloyl and p-coumaroyl acids linked via L-arabinose residues has been verified in several studies of xylan (6-8). The amounts of these components, however, are rather small. Every 15th arabinose unit in barley straw arabinoxylan is estimated to be esterified with ferulic acid, and every 31st with p-coumaric acid (7). These hydroxycinnamic acids are bound to C-5 of the arabinose residue (7, 8). It has been suggested that oxidative dimerization of ferulic acid residues crosslinks the arabinoxylan chains and renders them insoluble as a result of the diferuloyl bridges (9). 

The extent of inhibition of the oxidation of peroxidase substrates by ferulic salts was quite variable, from no inhibition to total inhibition. Total inhibition occurred when the substrate (e.g., syringaldazine) was closely related to ferulic acid. The presence of a fluorine atom in ferulic acid slightly reduced the inhibitory effect. Oxidation of ferulic compounds was restricted to lignifying cell walls in situ. Cell wall peroxidases from bark and xylem were fractionated into their component isozymes. 

Oxidation of Salts from Ferulic and / -Fluoroferulic Acids. When stem sections were incubated with ferulic acid, isopropylamine or sodium salts, the cell walls of the youngest xylem or sclerenchyma elements were stained a light pink color. No reaction was observed in other cell walls (Table I). The same result was obtained with fluorinated analogues. The fact that only peroxidases from lignifying cell walls are able to oxidize ferulic compounds and syringaldazine must be emphasized. Absorption spectra of the pink oxidation products of ferulic acid and / -fluoroferulic acid in the presence of hydrogen peroxide and peroxidases extracted from tobacco cell walls ( covalently bound fraction) showed a peak at 520 nm. 

Thus ferulic acid, which is not in vivo a natural substrate for peroxidases involved in lignification processes, can be oxidized not only in vitro but also in situ, i.e., in the normal, biological environment of the enzyme. Furthermore, the oxidation seems to be limited to the walls of lignifying cells. This restricted localization has been described only in the case of syringaldazine, a synthetic substrate closely related to cinnamic compounds... 

Table I. Staining Relative Intensity Observed in Tobacco Stem Sections Incubated with Different Peroxidase Substrates. Transverse sections were incubated with H2O2 and a peroxidase substrate. The oxidation of routinely used commercial substrates was checked in the presence or the absence of ferulic acid salts. Variations of staining intensity in cell walls (— to ++) were judged by observation with a light microscope...

Once the four anionic fractions were isolated (Bi, B2, Xi, X2), their activities were investigated using ferulic or / -fluoroferulic isopropylamine salts as substrates. Rates were plotted as a function of substrate concentration. The Lineweaver-Burk plots obtained (Fig. 4) were not always strictly linear as already reported in the case of ferulic acid and scolopetin oxidation (10,11)- An estimation was made of the apparent Km using the linear part of the plots and results were compared with those obtained for TMB. The values found in this case were in the same order of magnitude, about 0.5 X 10-3 to 1 x 10-3 M. In all extracts, / -fluoroferulic salt inhibited enzyme activity for concentrations higher than 0.25 X 10-2 M. 

A strong inhibition occured with TMB and syringaldazine. For instance, syringaldazine oxidation could be completely inhibited with ferulic acid either in situ (Table I) or in vitro. Inhibition of syringaldazine and TMB oxidations was noticeably weaker when / -fluoroferulic salt was used instead of ferulic salt. 

The activity of isoperoxidases able to oxidize ferulic acid is not restricted to a few similar substrates such as syringaldazine or TMB. A wider range of substrates are involved (3). Syringaldazine-oxidases from poplar and sycamore are known to react at least with TMB, PPD-PC and guiacol, but their affinity towards the last substrate is 100 to 1000 times lower than for syringaldazine (5,7,9). Similar results were obtained with other materials (12-14). However, other isozymes are not able to react with ferulic acid or syringaldazine (5,7,12,13). 

Figure 4. Double reciprocal plots of the relation between oxidation rate (V) and substrate concentration (S). The substrates were isopropylamine salts from / -fluoroferulic acid (A and B) and ferulic acid (C and D). A and C xylem isoperoxidase Xi, B and D xylem isoperoxidase X2. 

Laccase Oxidation of ferulic acid in sodium phosphate buffer/ethyl acetate to yield colorants [71]... 

After oral administration of caffeic acid to rats, small amounts of vanillic acid and vanilloylglycine are excreted. The conversion of p-hydroxycinnamic acid into /7-hydroxybenzoic acid is found in rat liver mitochondria [18], Studies with /7-hydroxy[U-14C]cinnamic acid have showed that 14C02 is released during reaction, indicating that reaction probably followed the p-oxidation type reactions, the two carbon being first removed as acetyl-CoA, and then oxidized to C02. It is assumed that conversion of ferulic acid formed by methylation of caffeic acid into vanillic acid occurs in rat liver mitochondria. 

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