Inhibition of cell wall peroxidases

Inhibition of Cell Wall Peroxidases with Ferulic Salts and Fluorinated Analogues... 

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. 

Varner, 1988). Extensin is secreted as single soluble monomeric hydroxyproline forms that are slowly insolubilized in the cell wall, probably via the oxidative formation of isodityrosine cross-links (Cooper and Varner, 1983 Fry, 1986a). Wall-catalyzed cross-linking of soluble extensin is inhibited by ascorbate, indicating that this reaction is dependent on an oxidative mechanism (Cooper and Varner, 1984). Thus, it is probable that a cell wall-bound peroxidase-ascorbate oxidase system controls the redox state at the wall, and hence the extensibility of cell wall, by controlling the cross-linking of wall glycoproteins. 

Isoniazid (INH) is a synthetic derivative of isonico-tinic acid. It has bactericidal activity against both intra- and extra-cellular mycobacteria. It also displays anti-bacterial activity in caseous lesions, but only in proliferating cells. Losing genes which code for catalase and peroxidase is the major mechanism through which resistance occurs. Single mutations can rapidly result in such resistance if isoniazid is used alone. Its mechanism of action is presumably based on inhibition of the synthesis of mycolic acids, unique and essential components of the mycobacterial cell wall. 

The plasma membranes of plant cells possess several redox activities that can be related to both plant nutrition and cell wall formation and lignification (Liithje et al., 1997 Berczi and Mpller, 2000). In this context, it has been shown that in oat roots, HMS humic fractions inhibited NADH oxidation in either the presence or absence of an artificial electron acceptor (ferricyanide), whereas LMS fractions inhibited this oxidase only if the electron donor (NADH) and acceptor (ferricyanide) were added at the same time (Pinton et al., 1995). While the first effect could be related to the activity of surface peroxidases that can be involved in cell wall formation and thickening (Vianello and Macri, 1991), the second seems to be exerted on a different redox system with an unknown function (Nardi et al., 2002). 

Isoniazid interferes with mycolic acid synthesis by inhibiting an enoyl reductase (InhA) which forms part of the fatty acid synthase system in mycobacteria. Mycolic acids are produced by a diversion of the normal fatty acid synthetic pathway in which short-chain (16 carbon) and long-chain (24 carbon) fatty acids are produced by addition of 7 or 11 malonate extension units from malonyl coenzyme A to acetyl coenzyme A. InhA inserts a double bond into the extending fatty acid chain at the 24 carbon stage. The long-chain fatty acids are further extended and condensed to produce the 60-90 carbon (3-hydroxymycolic acids which are important components of the mycobacterial cell wall. Isoniazid is converted inside the mycobacteria to a free radical species by a catalase peroxidase enzyme, KatG. The active free radicals then attack and inhibit the enoyl reductase, InhA, by covalent attachment to the active site. 

Isoniazid is bacteriostatic for resting bacilli but bactericidal for dividing microorganisms. Isoniazid is a prodrug that is converted by mycobacterial catalase-peroxidase into an active metabolite. It inhibits biosynthesis of my colic acids—long, branched lipids that are attached to a unique polysaccharide in the mycobacterial cell wall. Mycolic acids are unique to mycobacteria. The target of the isoniazid derivative is enoyl-ACP reductase of fatty acid synthase II, which converts unsaturated to saturated fatty acids in mycolic acid biosynthesis. 

The total number of polypeptides in the culture medium was 8-20 bands according to electrophoretic analysis (Figure 1). The protein export was inhibited by actinomycin D, cycloheximide, 2-deoxy-D-glucose and also by concanavalin A (Con A). In the presence of Con A (400 pg/ml), the enzymes were accumulated entirely inside the cells but not in the periplasm or the cell wall (Figure 2). At the same time the lectin had no influence upon cell growth and expression of invertase and acid phosphatase associated with the cell envelope. The activity accumulated inside Con A - treated cells was released into the culture medium on a-methylmannoside addition (Figure 3). The process was not affected by cycloheximide but was inhibited by sodium azide. The effect of Con A appears to be conditioned by its interaction with the plasma membrane of intact cells. Besides Con A, we detected peroxidase interaction with the plasmalemma of intact cells and alkaline phosphatase internment under physiological conditions. 

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