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.

Epidemiological studies have clearly demonstrated a link between dietary carotenoids and the reduced incidence of certain diseases, including some cancers. However recent intervention studies (e.g. ATBC, CARET and others) have shown that beta-carotene supplementation has little or no beneficial effect and may, in fact, increase the incidence of lung cancers in smokers. This presents a serious dilemma for the scientific community - are carotenoids at high concentrations actually harmful in certain circumstances? Currently, a significant number of intervention studies are on-going throughout the world involving carotenoids (of both natural and synthetic origin). Our approach has been to study the ability of supplementary carotenoids in protecting cells against oxidatively-induced DNA damage (as measured by the comet assay), and membrane integrity (as measured by ethidium bromide uptake). Both lycopene and beta-carotene only afforded protection against DNA damage (induced by xanthine/xanthine oxidase) at relatively low concentrations (1-3 microM). These levels are comparable with those seen in the plasma of individuals who consume a carotenoid-rich diet. However, at higher concentrations (4-10 microM), the ability to protect the cell against such oxidative damage was rapidly lost and, indeed, the presence of carotenoids may actually serve to increase the extent of DNA damage. Similar data were obtained when protection against membrane damage was studied. This would suggest that supplementation with individual carotenoids to significantly elevate blood and tissue levels is of little benefit and, may, in fact, be deleterious. This in vitro data presented maybe significant in the light of recent intervention trials.

No abstract

The model quinone compound menadione has been used to study the effects of oxidative stress in mammalian cells, and to investigate the mechanism of action of the quinone nucleus which is present in many anti-cancer drugs. We have used the alkaline single cell gel electrophoresis assay (comet assay) to investigate the effects of low doses of this compound on isolated human lymphocytes. We found that concentrations of menadione as low as 1 microM were sufficient to induce strand breaks in these cells. Pre-incubation with the NAD(P)H quinone oxidoreductase inhibitor dicoumarol, enhanced the production of menadione-induced strand breaks. In contrast, the metal ion chelator 1,10-phenanthroline inhibited formation of strand breaks, although prolonged incubation with 1,10-phenanthroline in combination with menadione resulted in an increase in a population of very severely damaged nuclei. A marked variation in the response of lymphocytes from different donors to menadione, and in different samples from the same donor was also observed.

The microbial degradation of cholic acid by Pseudomonas sp. N.C.I.B. 10590 was studied, and two major products were isolated and identified as 7 alpha, 12 beta-dihydroxyandrosta-1,4-diene-3,17-dione and 7 alpha, 12 alpha-dihydroxy-3-oxopregna-1,4-diene-20-carboxylic acid. Four minor products were isolated and evidence is given for the following structures: 7 alpha, 12 alpha-dihydroxyandrosta-1,4-diene-3,17-dione, 12 beta-hydroxyandrosta-1,4,6-triene-3,17-dione, 7 alpha, 12 beta, 17 beta-trihydroxyandrosta-1,4-dien-3-one and 7 alpha, 12 alpha-dihydroxy-3-oxopregn-4-ene-20-carboxylic acid. The significance of the production of the steroid products is discussed, along with the possible enzymic mechanisms responsible for their production.