Organocatalysts, low-molecular mass organic compounds composed of nonmetallic elements, are often used in organic synthesis, but there have been no reports of organocatalysts of biological origin that function in vivo. Here, we report that actinorhodin (ACT), a natural product derived from Streptomyces coelicolor A3(2), acts as a biocatalyst. We purified ACT and assayed its catalytic activity in the oxidation of L-ascorbic acid and L-cysteine as substrates by analytical methods for enzymes. Our findings were as follows: (i) oxidation reactions producing H 2 O 2 proceeded upon addition of ACT to the reaction mixture; (ii) ACT was not consumed during the reactions; and (iii) a small amount (catalytic amount) of ACT consumed an excess amount of the substrates. Even at room temperature, atmospheric pressure, and neutral pH, ACT showed catalytic activity in aqueous solution, and ACT exhibited substrate specificity in the oxidation reactions. These findings reveal ACT to be an organocatalyst. ACT is known to show antibiotic activity, but its mechanism of action remains unknown. On the basis of our results, we propose that ACT kills bacteria by catalyzing the production of toxic levels of H 2 O 2 . We also screened various other natural products of bacterial, plant, and animal origins and found that several of the compounds exhibited catalytic activity, suggesting that living organisms produce and use these compounds as biocatalysts in nature.A catalyst is a substance that increases the rate of a chemical reaction but is not consumed in the reaction. Catalysts are classified as homogeneous or heterogeneous, and most of the major homogeneous catalysts are metal-containing catalysts. In general, enzymes and ribozymes, which are classified as homogeneous catalysts, are referred to as biocatalysts. Enzymes are large proteins that catalyze numerous reactions in living organisms whereas ribozymes are composed of RNA and are known to catalyze phosphoryl transfer reactions (involved in RNA selfsplicing), the formation of peptide bonds, and various other reactions (1-5). Organocatalysts, which are homogeneous catalysts, are low-molecular mass organic compounds derived from nonmetallic elements (e.g., carbon, oxygen, hydrogen, and nitrogen) (6). Organocatalysts are used in industry because they have the following advantages over metal-containing catalysts (7-10): (i) Organocatalysts exhibit catalytic activity under mild conditions (atmospheric pressure, room temperature, and neutral pH); (ii) disposal of depleted organocatalysts is inexpensive; (iii) environmental loads due to waste reaction mixtures containing organocatalysts are low; and (iv) the risk of product contamination by metal ions is low. Therefore, organocatalysts have been receiving much attention in the field of green chemistry (11).In our laboratory, we have been studying the metabolism of actinomycetes from both fundamental and applied points of view (12)(13)(14)(15). From Streptomyces, we discovered a previously unidentified enzyme, L-glutamate oxidase (EC 1.4.3...

To study the link between energy metabolism and secondary metabolism/morphological development in Streptomyces, knockout mutants were generated with regard to the subunits of the cytochrome oxidase supercomplex (CcO) in Streptomyces coelicolor A3(2). All mutants exhibited an identical phenotype: viable but defective in antibiotic production and cell differentiation when grown in both complex and minimal media. The growth yield of the CcO mutant was about half of that of the WT strain on glucose medium while both strains grew similarly on maltose medium. Intracellular ATP measurement demonstrated that the CcO mutant exhibited high intracellular ATP level. A similar elevation of intracellular ATP level was observed with regard to the WT strain cultured in the presence of BCDA, a copper-chelating agent. Reverse transcriptase PCR analysis demonstrated that the transcription of ATP synthase operon is upregulated in the CcO mutant. Addition of carbonylcyanide m-chlorophenylhydrazone, an inhibitor of ATP synthesis, promoted antibiotic production and aerial mycelia formation in the CcO mutant and BCDA-treated WT cells. We hypothesize that the deficiency of CcO causes accumulation of intracellular ATP, and that the high ATP level inhibits the onset of development in S. coelicolor.

Streptomyces and related bacteria produce a wide variety of secondary metabolites. Of these, many compounds have industrial applications, but the question of why this group of microorganism produces such various kinds of biologically active substances has not yet been clearly answered. Here, we overview the results from our studies on the novel function and role of Streptomyces metabolites. The diverged action of negative and positive influences onto the physiology of various microorganisms infers the occurrence of complex microbial interactions due to the effect of small molecules produced by Streptomyces. The interactions may serve as a basis for the constitution of biological community.