p‐Hydroxybenzoate synthase: A complex associated with mitochondrial membranes of roots of Cucumis sativus

Biosynthesis of p-Hydroxybenzoate from p-Coumarate and p-Coumaroyl-Coenzyme A in Cell-Free Extracts of Lithospermum erythrorhizon Cell Cultures

“…Since the general phenylpropanoid metabolism is localized in the cytosol (Hrazdina and Jensen, 1992), and shikonin biosynthesis in Lithospermum takes place in vesicles formed from the ER (Tsukada and Tabata, 1984;Yamaga et al, 1993), it appears plausible that the enzymes of p-hydroxybenzoate biosynthesis are localized in the cytosol of Lithospermum cells. This is in contrast with the results in other plant systems in which the enzymes of p-hydroxybenzoate biosynthesis are reported to be associated with glyoxysomes in castor beans (Kindl and Ruis, 1971), with mitochondrial membranes in Cucumis sativus (Hagel and Kindl, 1975); and with thylakoid membranes in a blue-green alga (Loffelhardt and Kindl, 1976).…”

“…via the COA esters. However, in vitro studies in a number of plant systems (Alibert and Ranjeva, 1971;Kindl and Ruis, 1971;Alibert et al, 1972;Hagel and Kindl, 1975;French et al, 1976;Loffelhardt and Kindl, 1976;Yazaki et al, 1991;Schnitzler et al, 1992) could supply no biochemical evidence for this hypothesis. No COA esters were identified as intermediates, and most studies reported that the reaction is not dependent on the addition of ATP and COA.…”

“…1) was given additional support after it was found that C1 and Cz of phenylpropanoid precursors are ' This work was supported by the Alfred Krupp-Forderpreis (to removed as acetate or acetyl-coA (Vollmer et al, 1965). However, most of the subsequent in vitro studies in cell-free plant extracts (Alibert and Ranjeva, 1971;Kindl and Ruis, 1971;Alibert et al, 1972;Hagel and Kindl, 1975;French et al, 1976;Loffelhardt and Kindl, 1976;Yazaki et al, 1991;Schnitzler et al, 1992) showed that the enzymatic conversion of phenylpropanoid precursors to benzoic acids was not dependent on addition of ATP and COA, which contradicts the @-oxidation mechanism.…”

“…It remains to be seen whether the pathway via the COA esters can be demonstrated in other plant systems, especially in those for which a different mechanism for the biosynthesis of benzoic acids has been proposed (French et al, 1976; Funk a n d Brodelius, 1990b;Schnitzler et al, 1992) or in which a different compartmentalization of the enzymes was observed (Kindl a n d Ruis, 1971; Hagel a n d Kindl, 1975; Loffelhardt a n d Kindl, 1976). Of special interest is the question of whether the biosynthesis of salicylic acid proceeds in a similar way.…”

Enzymic Synthesis of Lignin Precursors

“…One could assume that in vivo the cinnamoyl-CoA reductase and cinnamoyl alcohol dehydrogenase form an enzyme complex which might even include the pcoumarate : CoA ligase and other enzymes involved in the pathway to lignin precursors. Membrane-bound multienzyme systems have recently been found in the biosynthesis of hydroxycinnamic acids [37,38], benzoic acids [39,40], and a cyanogenic glycoside [41]. Even without an enzyme complex the cinnamaldehyde pool must be very small because of the very low K,,, value (10-1 p M ) of cinnamyl alcohol dehydrogenase for these substrates [lo, 111.…”