Summary
The amount of carbonyl groups in an organosolv lignin was determined by 19F NMR spectroscopy after
different derivatizations: derivatization with trifluoromethylphenylhydrazine, fluorobenzoylation of
alcohol groups formed after NaBH4 reduction of lignin, fluorobenzoylation of phenolic hydroxyl groups
after catalytic hydrogenation of lignin. Oximation was also used for comparison. Carbonyl group contents
determined by 19F NMR after trifluoromethylphenylhydrazine derivatization were in good correlation
with results from other methods. Trifluoromethylphenylhydrazine derivatization is a fast and easy
technique, which provides a distinct quantification of aldehyde, ketone and quinone groups. Some round
robin lignins (Milne et al. 1992), using trifluoromethylphenylhydrazine derivatization and modified oximation
(Zakis 1994) provided significantly higher carbonyl group contents than the round robin test data,
which had been measured either by classical oximation or by reduction-UV methods. Other recently
reported carbonyl group estimations on round robin lignins (Faix et al. 1998; Ahvazi et al. 1999) were
either in agreement or in disagreement with the herein-presented results. This indicates that carbonyl
group analysis in lignins is difficult and that care must be taken when selecting an appropriate method.
Alcaligenes eutrophus CH34 used benzoate as a sole source of carbon and energy, degrading it through the 3-oxoadipate pathway. All the enzymes required for this degradation were shown to be encoded by chromosomal genes. Catechol 1,2-dioxygenase activity was induced by benzoate, catechol, 4-chlorocatechol, and muconate. The enzyme is most likely a homodimer, with an apparent molecular weight of 76,000 +/- 500. According to several criteria, its properties are intermediate between those of catechol 1,2-dioxygenases (CatA) and chlorocatechol 1,2-dioxygenases (ClcA). The determined Km for catechol is the lowest among known catechol and chlorocatechol dioxygenases. Similar Km values were found for para-substituted catechols, although the catalytic constants were much lower. The catechol 1,2-dioxygenase from strain CH34 is unique in its property to transform tetrachlorocatechol; however, excess substrate led to a marked reversible inhibition. Some meta- and multi-substituted catechols behaved similarly. The determined Km (or Ki) values for para- or meta-substituted catechols suggest that the presence of an electron-withdrawing substituent at one of these positions results in a higher affinity of the enzyme for the ligand. Results of studies of recognition by the enzyme of various nonmetabolised aromatic compounds are also discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.