The metabolism of aromatic acids by micro-organisms. Metabolic pathways in the fungi

Abstract

1. The metabolic pathways of aromatic-ring fission were examined in a range of fungal genera that utilize several compounds related to lignin. 2. Most of the genera, after growth on p-hydroxybenzoate, protocatechuate or compounds that are degraded to the latter (e.g. caffeate, ferulate or vanillate), rapidly oxidized these compounds, but not catechol. 3. Such genera possessed a protocatechuate 3,4-oxygenase and accumulated beta-carboxymuconate as the product of protocatechuate oxidation. This enzyme had a high pH optimum in most organisms; the Rhodotorula enzyme was competitively inhibited by catechol. 4. beta-Carboxymuconate was converted by all competent fungi into beta-carboxymuconolactone, which was isolated and characterized. None of the fungi produced or utilized at significant rates the corresponding bacterial intermediate gamma-carboxymuconolactone. 5. The lactonizing enzymes of Rhodotorula and Neurospora crassa had a pH optimum near 5.5 and approximate molecular weights of 19000 and 190000 respectively. 6. The fungi did not degrade the isomeric (+)-muconolactone, gamma-carboxymethylenebutanolide or beta-oxoadipate enol lactone at significant rates, and thus differ radically from bacteria, where beta-oxoadipate enol lactone is the precursor of beta-oxoadipate in all strains examined. 7. The end product of beta-carboxymuconolactone metabolism by extracts was beta-oxoadipate. 8. Evidence for a coenzyme A derivative of beta-oxoadipate was found during further metabolism of this keto acid. 9. A few anomalous fungi, after growth on p-hydroxybenzoate, had no protocatechuate 3,4-oxygenase, but possessed all the enzymes of the catechol pathway. Catechol was detected in the growth medium in one instance. 10. A strain of Penicillium sp. formed pyruvate but no beta-oxoadipate from protocatechuate, suggesting the existence also of a ;meta' type of ring cleavage among fungi.

Regulation of Aromatic Metabolism in the Fungi: Metabolic Control of the 3-Oxoadipate Pathway in the Yeast Rhodotorula mucilaginosa

“…I) serves in many aerobic bacteria to transform catechol, protocatechuate and their respective precursors to succinate and acetyl-CoA. The regulation of the enzymes operative in this pathway has been extensively investigated in a number of species of Pseudomonas (Ornston, 1966a;Kemp & Hegeman, 1968;Stanier, 1968;RobertGero, Poiret & Stanier, 1969) and in Moraxella calcoacetica (Cgnovas & Stanier, 1967), Alcaligenes eutrophus (Johnson & Stanier, 1971) and several Nocardia species (Rann & A general survey of the routes utilized by fungi for the catabolism of aromatic compounds (Cain, Bilton & Darrah, 1968) confirmed the widespread existence of the 3-oxoadipate pathway within this group. In all the fungal genera examined the subsequent metabolism of the ring cleavage product, 3-carboxymuconate, proceeded through 3-carboxymuconolactone rather than through the 4-substituted isomer characteristic of the bacteria, confirming an earlier observation in Neurospora crassa (Gross, Gafford & Tatum, 1956).…”

Oxidation of Phenols by Yeast

“…HARRIS and RICKETTS (10 ) and CAIN et al ( 4 ) reported that the utilization of phenol for growth by some yeast strains occurred only after the cultivation of 1 to 2 weeks. In the present experiment, the growth of C. tropicalis on phenol was excellent compared with the growth on other carbon sources including catechol and methylcatechols, and reached a maximum value after 2 days' incubation.…”

“…Furthermore, FEIST and HEGEMAN (3) showed that the bacteria grown on phenol contained an enzyme which catalyzed the benzene ring cleavage by an extra-diol type fission, and that the bacteria grown on benzoate contained an enzyme which catalyzed the cleavage by an intra-diol type fission. CAIN et al (4) studied the oxidation of phenols that were related to lignin by various strains of fungi and yeasts using whole cells and cell-free extracts.…”

Enzymes of the 3-Oxoadipate Pathway in Fungi: A Serological Study of 3-Carboxymuconate Cyclase (Lactonizing Enzyme) in Fungi and its Possible Taxonomic Significance

“…The biochemistry of the pathway is similar in both groups of micro-organisms, although in all fungi the subsequent metabolism of the ring cleavage product, 3-carboxymuconate, proceeds through 3-carboxymuconolactone (Gross, Gafford & Tatum, 1956;Cain, Bilton & Darrah, 1968~) rather than through the 4-substituted isomer as in bacteria (Stanier & Ornston, 1973).…”