Conversion of xanthoxin to abscisic Acid by cell-free preparations from bean leaves

Cell-free extracts from the leaves of Phaseolus vulgaris L. convert xanthoxin to abscisic acid. The enzyme activity in dialyzed or acetone-precipitated extracts shows a strong dependence on either NAD or NADP. The enzyme activity appears to be cytosolic with no significant activity observed in chloroplasts. The activity was observed in extracts from roots of Phaseolus vulgaris, and also in extracts prepared from the leaves of Pisum sativum L., Zea mays L., Cucurbita maxima Duchesne, and Vigna radiata L. Neither water stress nor cycloheximide appear to significantly affect the level of enzyme activity in leaves. No intermediates between xanthoxin and abscisic acid were detected.     

Conversion of oxyhemoglobin to methemoglobin by organic and inorganic reductants

Human oxyhemoglobin is converted to methemoglobin by a wide array of organic and inorganic reductants. Depending upon the concentration and nature of the reductant, varying amounts of deoxyhemoglobin are produced. The general overall sequence is: FeO2 leads to (1) FeIII leads to (2) FeII. The intermediacy of methemoglobin can be demonstrated by direct spectral observation and by cyanide trapping. For organic reductants, the second-order rate constants for (1) vary from greater than 300 (phenylhydroxylamine) to 1.4 X 10(-4) M-1 s-1 (malononitrile). Generally the rates parallel the ease of hydrogen abstraction by iron-bound oxygen from the substrate, and simply hydrocarbons are reactive. Rates for these processes have been ascertained with recrystallized protein, lysed cells, and intact human erythrocytes. At room temperature oxyhemoglobin quantitatively converts benzaldehyde to benzoic acid and hydroquinone to benzoquinone. Rates for inorganic species (process 1) range from greater than 7 X 10(3) (chromous ion) to 0.015 M-1 s-1 (ferrocyanide). Ferrous ion rapidly deoxygenates oxyhemoglobin by direct attack on the oxy complex but methemoglobin is not an intermediate with this reagent. Taken together the results support the theoretical prediction that reductants should oxidize oxyhemoglobin, and they demonstrate at least some degree of radical character to the oxy complex.     

Conversion of emodin to physcion by a cell-free preparation of Aspergillus parasiticus

Cultures of Aspergillus parasiticus contained 1.2 mg/litre of physcion. A cell-free extract of a 3-day-old culture of A. parasiticus catalysed the conversion of [³H]emodin and S-adenosyl-L-[Me-¹⁴C]methionine to ³H- and ¹⁴C-labelled physcion. Methylation of emodinanthrone was 9% of the methylation of emodin. Methylation of norsolorinic acid or versicolorin A, compounds associated with aflatoxin biosynthesis, was not detected.