Wood products carboxylic acid groups

Reaction 3.1, the key reaction of propionic acid fermentation, is catalyzed by pyruvate carboxytransphosphorylase, a unique biotin-dependent transcarboxylase (see below). There are other reactions of carboxyl group transfer catalyzed by phosphoenolpyruvate (PEP) carboxytransphosphorylase and phosphoenolpyruvate carboxykinase, but these (i) do not require biotin and (ii) use CO2 as the source of carboxyl groups. The actual species involved may be HCO3" (or H2CO3) rather than free CO2 (Cooper et al., 1968), since free CO2 is not evolved in the PEP carboxytransphosphorylase reaction (Swick and Wood, 1960). Propionic acid bacteria are able to decarboxylate succinate, producing CO2 in a biotin-dependent reaction (Delwiche,1948 Lichstein, 1958). If succinate is accumulated as the end product, then the cycle (see Fig. 3.1) is broken, and oxaloacetic acid is not supplied by reaction 3.1, but is formed primarily by CO2 fixation onto PEP catalyzed by PEP carboxytransphosphorylase (PEP-CTP). 

COs to form oxalacetate which under anaerobic conditions is reduced to malate. The malate in turn may be converted to fumarate and succinate (Fig, 5). The last step in this series of reactions is blocked by malonate. The second pathway involves the aerobic condensation of pyruvate and oxalacetate followed by oxidation of the condensation product to form -ketoglutarate and succinate. Wood has proposed that the first condensation product of the aerobic tricarboxylic cycle is cfs-aconitic acid which is then converted to succinate by way of isocitric, oxalosuccinic, and a-ketoglutaric acids. The a-ketoglutarate is decarboxylated and oxidized to succinic acid. Isotopic a-ketoglutarate containing isotopic carbon only in the carboxyl group located a to the carbonyl would be expected to yield non-isotopic succinate after decarboxylation. This accounts for the absence of isotopic carbon in succinate isolated from malonate-poisoned liver after incubation with pyruvate and isotopic bicarbonate. 

Uronic Acid. Uronic acid is determined by measuring carbon dioxide (CO2) generation when wood is boiled with 12% HCl (45). Results from this method may be somewhat high because of CO2 evolution from material containing carboxyl groups other than uronic acid. A method developed by Scott (46) is rapid and selective. The sample is treated with 96% H2SO4 at 70 °C, and a product, 5-formyl-2-furancarboxylic acid, is derived from uronic acids. This compound reacts selectively with 3,5-dimethylphenol to yield a chromophore absorbing at 450 nm. 

Fundamentally similar to pyrromethene formation are two of the classical colour reactions associated with pyrroles. The redness produced by pyrroles with an acid-moistened pine shaving is due to reaction with aldehydes in the wood, but it is not specific for pyrroles " . Ehrlich s reaction depends on the formation of coloured products by the reaction of a pyrrole with j -dimethylaminobenzaldehyde in acid solution. The nature of the reaction is indicated by the isolation of a salt of the cation (26) after treatment of (27) with the Ehrlich reagent, a carboxyl group being eliminated (26) gives red solutions, the disodium salt of the derived free base produces yellow solutions, and treatment of (26) with excess acid the colourless di-protonated salt . ... 

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