Enzymatic description of the anhydrofructose pathway of glycogen degradation; I. Identification and purification of anhydrofructose dehydratase, ascopyrone tautomerase and alpha-1,4-glucan lyase in the fungus Anthracobia melaloma.

The anhydrofructose pathway describes the degradation of glycogen and starch to metabolites via 1,5-anhydro-d-fructose (1,5AnFru). The enzyme catalyzing the first reaction step of this pathway, i.e., alpha-1,4-glucan lyase (EC 4.2.1.13), has been purified, cloned and characterized from fungi and red algae in our laboratory earlier. In the present study, two 1,5AnFru metabolizing enzymes were discovered in the fungus Anthracobia melaloma for the formation of ascopyrone P (APP), a fungal secondary metabolite exhibiting antibacterial and antioxidant activity. These are 1,5AnFru dehydratase (AFDH) and ascopyrone tautomerase (APTM). AFDH catalyzed the conversion of 1,5AnFru to ascopyrone M (APM), a compound that has been earlier presumed to occur biologically, while APTM isomerized the APM formed to APP. Both enzymes were purified 400-fold by (NH(4))(2)SO(4) fractionation, hydrophobic interaction, ion-exchange and gel filtration chromatography. The purified AFDH showed a molecular mass of 98 kDa on SDS-PAGE and 230 kDa by gel filtration. The corresponding values for APTM was 60 and 140 kDa. Spectrophotometric and HPLC methods were developed for the assay of these two enzymes. To confirm that A. melaloma possessed all enzymes needed for conversion of glycogen to APP, an alpha-1,4-glucan lyase from this fungus was isolated and partially sequenced. Based on this work, a scheme of the enzymatic description of the anhydrofructose pathway in A. melaloma was proposed.