The role of dihydropsoralen in furanocoumarin metabolism

Trapping experiments with [2-14C]umbelliferone and 2′,3′-dihydropsoralen (DHP) administered to Ruta graveolens yielded negative results over metabolic periods of 5–24 h. Specific radioactivities of psoralen were comparable to those previously observed, but those of DHP were about two orders of magnitude lower. These results do not support the theory (Z. Naturforsch. 25b, 700 (1970)) that DHP is the immediate precursor of psoralen in furanocoumarin biosynthesis, and it is proposed instead that DHP is not on the main pathway, but is in an equilibrium with psoralen that greatly favors dehydrogenation.

Comparison of (+)- and (-)-marmesin as intermediates in the biosynthesis of linear furanocoumarins

Marmesin has been identified by chromatography and ultraviolet absorption spectrum in extracts of Ruta graveolens, in confirmation of earlier conclusions from tracer experiments that it is an intermediate in furanocoumarin biosynthesis in this species. Trapping experiments with [2-14C]umbelliferone and (+)- or (−)-marmesin were inconclusive, but indicated that only the (+)-form is metabolically active in R. graveolens. This was confirmed in Ruta and also in Heracleum lanatum and Angelica archangelica by direct comparison feedings of [3-14C](+)- and (−)-marmesin. The (+)-isomer was an efficient furanocoumarin precursor, as before, while little if any utilization of (−)-marmesin could be demonstrated.

The metabolism of 2-furoic acid by Pseudomanas F2

1. Pseudomonas F2 isolated by enrichment culture on 2-furoic acid and grown with it as carbon source oxidized the compound with a Q(o) (2) of 170mul./mg. dry wt./hr. and the overall consumption of 2.5mumoles of oxygen/mumole of substrate. 2. In the presence of 1mm-sodium arsenite, oxygen uptake was restricted to 0.54mumole/mumole of 2-furoate oxidized, with the formation of 0.86mumole of 2-oxoglutarate/mumole of 2-furoate. 3. Cell suspensions, disrupted in a French pressure cell and centrifuged at 27000g, yielded supernatants capable of catalysing the slow oxidation of 2-furoate (0.17mumole/mg. of protein/hr.). 4. Fractionation of 27000g supernatants at 200000g yielded a soluble enzyme fraction capable of catalysing the oxidation of 2-furoate only in the presence of added 200000g pellet or of Methylene Blue. 5. The 2-furoate-stimulated uptake of oxygen or the anaerobic reduction of Methylene Blue by dialysed 27000g supernatant required the addition of ATP and CoA, and the rate of oxygen uptake was further enhanced by the addition of magnesium chloride and NAD(+). 6. The role of ATP and CoA in the formation of 2-furoyl-CoA was demonstrated by the accumulation of 2-furoylhydroxamic acid in the presence of hydroxylamine. 7. Dialysed 200000g supernatant, treated with Dowex 1, required the addition of ATP, CoA and Methylene Blue before it could oxidize 2-furoate to 2-oxoglutarate, which was trapped in unitary stoicheiometric yield as its phenylhydrazone. Magnesium chloride and NAD(+) were not stimulatory in this system. The oxidation of 2-furoate to 2-oxoglutarate was not inhibited by substrate analogues, metal ion-chelating agents, thiol-active compounds or inhibitors of cytochrome-mediated electron transport. 8. No evidence was obtained for the intervention of 2,5-dioxovalerate as an intermediate in 2-oxoglutarate formation.