Natural low molecular mass organic compound shows catalytic activity

Abstract

Organocatalysts are catalysts being low molecular mass organic compounds derived from non‐metal elements. However, there is no report that organocatalysts of biological origins function in vivo. Here we report that the “natural” product, actinorhodin (ACT), produced by Streptomyces coelicolor A3(2) acts as a biocatalyst.
 During the screening of a new oxidase from streptomycetes, we found that supernatant of S. coelicolor A3(2) showed catalytic activity to oxidize l‐ascorbic acid (l‐ASC). The oxidase could not be purified, but, a correlation between the depth of color and the oxidase activity was obtained. We discovered that the addition of purified ACT to the reaction mixture containing l‐ASC as a substrate led to a decrease in the O2 concentration. We characterized ACT from enzymological standpoints. As a result, (i) oxidation reactions producing H2O2 proceeded on the addition of ACT to the reaction mixture; (ii) ACT was not consumed during the reactions; and (iii) a small amount of ACT consumed an excess amount of the substrates. Even under room temperature, atmospheric pressure and neutral pH, ACT showed catalytic activity in aqueous solution. ACT exhibited substrate specificity in the oxidation reactions. These findings reveal that ACT is discovered as a new member of organocatalyst. ACT is known as an antibiotic toward some microorganisms, but the action mechanism remains unknown. We also propose that bacterial death by ACT is caused by the toxicity of H2O2 produced.