No abstract

The dioxygenase produced by Aspergillus flavus that oxidizes quercetin contains 2 moles of copper per mole of enzyme and binds at least 2 moles of substrate. The enzyme is not inhibited by sulfhydryl reagents or affected by H2O2, but is inhibited by copper-chelating agents and reducing agents. Nitrogen bases with chelating ability are more effective inhibitors than those that do not form metal chelates.The dioxygenase oxidizes flavones that possess a double bond between carbons-2 and -3 and a hydroxyl on carbon-3. Hydroxyls at other positions affect both the relative rates of enzymatic oxidation and the concentration of substrate required to attain half maximal rate (Km). The evidence indicates that the substrate binds to the copper of the enzyme via the 3-hydroxyl and 4-carbonyl groups of the substrate. A possible mechanism for the reaction is presented.

The optimal growth pH and conditions necessary to give a full manifestation of the effect of reductants upon the growth of Campylobacter ,fetus were investigated using static cultivation. The multiplication of cells was limited to a narrow range of added reductants. Thioglycollate supplemented without heating produced heavy growth in combinations of 0.05% at pH 6.80 or 0.1% at pH 6.60, and 0.2% at pH 7.00 or 7.20. Although the stimulating effect depended upon the time between the addition of the supplement and inoculation, two prominent peaks in the growth curve always appeared with both alkaline and acidic pH ranges of the medium. Autoclaving the medium with some SH compounds brought about this growth only at around pH 6.50. Consequently there was a uniform decrease in the initial pH. L-Cysteine and ascorbic acid also gave similar effects. Glucose remarkably prevented the growth promotion due to SH compounds. Optimal initial reduction potential for growth in a semisolid medium was considered to be-0.05 to-0.08 volt at an initial pH of 6.60. SH compounds supplemented without heating brought about a marked longevity of the culture in comparison with a culture in an autoclaved medium of the same composition. For the growth of C. fetus in semisolid medium, it was important to avoid decreasing the growth-promoting activity of some of the supplemented SH compounds by not heating but adding the supplement aseptically. Also a rigid regulation of the pH, the concentration of the added reductants, and the time of inoculation into the fresh medium were important.

No abstract

MILLS. 1971. Degradation of rutin by Aspergillr~s pavrts. Purification of the dioxygenase, quercetinase. Can. J. Microbiol. 17: 11 1-1 18. Evidence is presented that a single enzyme, quercetinase, is responsible for the degradation of quercetin by Aspergillus flavlts to yield carbon monoxide and a depside, 2-protocatechuoylphloroglucinol carboxylic acid. A procedure for the isolation of the dioxygenase as a homogeneous protein is described. The most purified preparation degraded 10 800 umoles of quercetin/h mg protein and was homogeneous as judged by ultracentrifugation and by electrophoresis. The molecular weight was determined as 111 000 + 4000. K,,, values for quercetin and oxygen as substrates were 5.2 X 1 0 -W and 1.2 X 10-4 M respectively. The enzyme is a glycoprotein containing 27.5% carbohydrate and the amino acid composition is presented.