Additional survey on genotoxicity of natural anthraquinones in the hepatocyte primary culture/DNA repair assay

Genotoxicity of fungal anthraquinones of islandicin, iridoskyrin and (-) rubroskyrin, and a colorant of insect origin, cochineal and its component, carminic acid, an anthraquinone, was examined in the hepatocyte primary culture/DNA repair test. The results were compared with that of versicolorin A, an anthraquinone with bisfuran ring, which had been proved to be genotoxic on this assay. All of these anthraquinones, differently from versicolorin A did not show clear response of DNA repair. The results suggest that these agents are not genotoxic carcinogens.

A novel anthraquinone ring cleavage enzyme from Aspergillus terreus

An enzyme activity which catalyzes the ring cleavage of the anthraquinone questin to form benzophenone desmethylsulochrin was found in the cell-free extract of Aspergillus terreus, a (+)-geodin producer. The product was identified as desmethylsulochrin by high-resolution mass spectroscopy and chemical carrier dilution analysis. The enzyme showed an absolute requirement of NADPH and molecular oxygen. Therefore, the enzyme, named questin oxygenase, was considered to be classified as a monooxygenase. The optimum pH was around 7.5. The enzyme was very unstable and lost its activity completely after storage overnight at 4 degrees C in 0.05 M phosphate buffer, pH 7.5. The instability of the questin oxygenase was partially overcome by the addition of polyols and the non-ionic detergent Tween 80 to the buffer. By DEAE-cellulose column chromatography, two protein fractions, named DE-I and DE-II, were obtained. Neither fraction reacted with questin by itself. However, the combination of DE-I and DE-II reconstituted the questin oxygenase system to convert questin to desmethylsulochrin. This result suggested that the system is not a simple combination of oxygenase and hydrolase, but requires some additional factor(s) such as electron transfer protein.

Purification and properties of dihydrogeodin oxidase from Aspergillus terreus

The last step of (+)-geodin biosynthesis is a phenol oxidative coupling, which is one of the most important reactions in biosynthesis of natural products. The enzyme named dihydrogeodin oxidase catalyzes the regio- and stereospecific phenol oxidative coupling reaction to form (+)-geodin from dihydrogeodin. The enzyme was purified from the cell-free extract of Aspergillus terreus, a (+)-geodin producer, by ammonium sulfate fractionation, acid treatment, and column chromatographies on DEAE-cellulose, Hydroxyapatite, chromatofocusing, and Toyopearl HW-55S. The purified enzyme was homogeneous as judged by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The molecular weight of the enzyme was estimated to be 153,000 by gel filtration on a Toyopearl HW-55S column and 76,000 by SDS-polyacrylamide gel electrophoresis, indicating that the enzyme is a dimer. The purified enzyme showed an intense blue color and had absorption maxima at 280 and 600 nm, which suggested it to be a blue copper protein. The copper content was found to be 8 atoms per subunit by atomic absorption analysis and no significant amount of other metals was detected by ICP emission spectrometry. The electron paramagnetic resonance spectrum showed the presence of type 1 and type 2 copper atoms in the enzyme molecule. Sodium azide and ethylxanthate inhibited the enzyme activity, but potassium cyanide and diethyldithiocarbamate, both known as potent copper enzyme inhibitors, were not inhibitory.

Purification and some properties of chalcone synthase from a carrot suspension culture induced for anthocyanin synthesis and preparation of its specific antiserum

Chalcone synthase was purified to homogeneity by polyacrylamide gel electrophoresis from cell suspension cultures of carrot in which anthocyanin synthesis was induced by transferring the cells from a medium containing 2,4-dichlorophenoxy-acetic acid (2,4-D) to one lacking it. A molecular weight of 80,000-85,000 for the enzyme was determined by gel filtration and disc-gel polyacrylamide electrophoresis, and one of about 40,600 for the subunit by SDS slab-gel electrophoresis. The primary reaction product was chalcone and the pH optimum of the reaction was 8.0. The Km values for 4-coumaroyl-CoA and malonyl-CoA were 5.7 microM and 18 microM, respectively. These properties of carrot chalcone synthase were discussed in comparison to those of that from cell cultures of parsley reported previously. Antiserum against chalcone synthase from carrot was obtained from mice bred under specific pathogen free conditions. Crossreactivity was examined by Western-blotting, and the high specificity of the antiserum against chalcone synthase was demonstrated.

Interaction of digitonin and its analogs with membrane cholesterol

The interaction of digitonin with membrane cholesterol was studied by using various digitonin analogs, and radioactive desglucodigitonin. The following results were obtained concerning the effect of digitonin on erythrocytes, granulocytes and liposomes. Digitonin and its analogs showed activity to induce hemolysis, granulocyte activation and liposomal membrane damage. The activity was affected by change of the carbohydrate residue of the molecule; the order of hemolytic activity was digitonin greater than or equal to desglucodigitonin much greater than glucosyl-galactosyl-digitogenin greater than galactosyl-digitogenin, digitogenin. The relative activities of these compounds to induce granulocyte activation and liposomal membrane damage were similar to those observed in the hemolysis. [3H]Desglucodigitonin could bind to cholesterol in liposomes. The binding was stoichiometric and the ratio of desglucodigitonin bound to liposomes/cholesterol in liposomes was close to 1, irrespective of the cholesterol content in liposome. Damage to liposomes was, however, induced by desglucodigitonin only when they contained more than 0.2 molar ratio of cholesterol to phospholipid. Addition of digitonin as well as desglucodigitonin to preformed liposomes deprived of cholesterol affected the anisotropic molecular motion of spin-labeled phosphatidylcholine incorporated into the liposomes, suggesting that the molecules could be inserted into the lipid bilayer free of cholesterol. Molecules of desglucodigitonin in the lipid phase may, however, be equilibrated with those in the aqueous phase, unless they form a complex with cholesterol, since no appreciable amount of [3H]desglucodigitonin could be detected in the liposome fraction after separation by column chromatography. Digitonin decreased the order parameter of spin-labeled phosphatidylcholine when liposomes contained equimolar cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)