Discovery of soraphen A from myxobacteria was an important event in antifungal metabolite development, because of not only enlarging microbial diversity as a source of antifungal compounds but also introducing fungal ACC as a novel target for antifungal agent screening (Gerth et al. 1994). Acetyl-CoA carboxylase catalyzes carboxylation of acetyl-CoA to malonyl-CoA at the expense of ATP. While the functional units of ACC are usually separate proteins in prokaryotes, they form a multifunctional enzyme complex in eukaryotes. This may be the reason why soraphen A is inactive to bacteria. Soraphen A which is mainly responsible for antifungal activity of Sorangium cellulosum strain Soce26 effectively controlled powdery mildew (Erysiphe graminnis f. sp. hordei) in barley, snow mold (Gerlachia nivalis) in rye, apple scab (Venturia inaequalis) on apple and gray mold (B. cinerea) on grape (Reichenbach and Hofle 1995). Soraphen A has no effect on ACC of plants, thus inducing no phytotoxicity in the field (Vahlensieck et al. 1994). In contrast, ACC from rat liver was strongly inhibited by the soraphen (Pridzun et al. 1995). Due to the risky side effects on experimental animals, soraphen A has not been practically used for control of plant diseases. However, the results of soraphen research strongly suggest that fungal ACC could be a target site for antifungal agent screening. Considering the numerous diversity of natural products related to the specificity of ACC, novel biofungicides from microbial metabolites that block specifically the activity of fungal ACC may be developed in the future.
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