0-Fluoroferulic acid

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. 

Figure 1. Chemical structure of ferulic acid (left) and / -fluoroferulic acid (right).

Figure 2. Anion exchange chromatogram of ionically bound phloem peroxidases on DEAE-Sepharose. Collected fractions were analyzed for their oxidase activity towards TMB (1), syringaldazine (2) and isopropylamine salt from / -fluoroferulic acid (3). Bo cationic peroxidases Bj and B2 anionic peroxidases. Column was equilibrated with 0.01 M phosphate buffer (pH 7.1). Fractions were eluted with a NaCl gradient (0-0.5 M) in the same buffer (0.01 M phosphate, pH 7.1).

Inhibition of Commercial Synthetic Substrates with Salts from Ferulic and j3-Fluoroferulic Acids. Table I summarizes the results obtained on stem sections incubated in a medium containing one of the usual commercial substrates and a salt of ferulic or / -fluoroferulic acid. Three types of interactions could be observed ... 

No inhibition, or only a very slight one, could be seen on sections incubated in a PPD-PC medium. Absorption spectra did not show much difference when ferulic or / -fluoroferulic acid were added to the assay mixture. 

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. 

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. 

---