Antrimycin B

The light reactions of photosynthesis are known to comprise both linear and cyclic electron flow in order to convert light energy into chemical energy in the form of NADPH and ATP. Antimycin A (AA) has been proposed as an inhibitor of ferredoxin-dependent cyclic electron flow around photosystem I (CEF-PSI) in photosynthesis research. However, its precise inhibitory mechanism and target site had not been elucidated yet. Here we show that AA inhibits the cyclic (alternative) electron flow via cytochrome b559 (Cyt b559) within photosystem II (CEF-PSII). When AA was applied to thylakoid membranes isolated from spinach leaves, the high potential form of Cyt b559, which was reduced in the dark, was transformed into the lower potential forms and readily oxidized by molecular oxygen. In the absence of AA, the reduced Cyt b559 was oxidized by P680+ upon light illumination and re-reduced in the dark, mainly by the electron from the QB site on the acceptor side of PSII. In contrast, AA suppressed the oxidation of Cyt b559 and induced its reduction under the illumination. This inhibition of Cyt b559 oxidation by AA enhanced photoinhibition of PSII. Based on the above results, we propose caution regarding the use of AA for evaluating CEF-PSI per se and concurrently propose that AA provides for new insights into, and interpretations of, the physiological importance of Cyt b559, rather than that of CEF-PSI in photosynthetic organisms.

Colorectal cancer is the third most life-threatening cancer in the western countries. For the treatment, several chemotherapeutic drugs are using those that have severe side effects on the patient. So, finding alternative drugs is important. In the present research antimycin A was selected to evaluate the anticancer properties on the HCT-116 colorectal cancer cells. Antimycin A inhibited HCT-116 cells proliferation with the IC50 value of 29 µg/mL concentration. As a long-term effect, HCT-116 cells were incubated with 10-40 µg/mL concentration of antimycin A for 7 days. No colony was observed in the treated wells. Apoptotic features in HCT-116 cells were observed in antimycin A treated cells after being stained with Hoechst 33342 dye. Apoptosis was further confirmed by FITC-annexin V/PI. Role of caspase-3 protein in the apoptosis process was also confirmed by the caspase-3 inhibitor. After treatment of HCT-116 cells with antimycin A, apoptotic related gene expression was checked by reverse transcription polymerase chain reaction. p53 and caspase-9 genes were upregulated consequently mitogen-activated protein kinases (MAPK), poly(ADP-Ribose) polymerase (PARP), and nuclear factor kappa B (NF-κB) genes were downregulated. Molecular docking simulation indicated significant binding affinity of antimycin A with the five proteins. The results indicated antimycin A would be a promising anticancer agent for further anticancer research.

Marine actinomycetes are prolific chemical sources of complex and novel natural products, providing an excellent chance for new drug discovery. The chemical investigation of the marine-derived Streptomyces sp. ITBB-ZKa6, from Zhaoshu island, Hainan, led to the discovery of two unique antimycin-type depsipeptides, zhaoshumycins A (1) and B (2), along with the isolation of the four known neoantimycins A (3), F (4), D (5), and E (6). The structures of the new compounds 1 and 2 were elucidated on the basis of the analysis of diverse spectroscopic data and biogenetic consideration. Zhaoshumycins A (1) and B (2) represent a new class of depsipeptides, featuring two neoantimycin monomers (only neoantimycin D or neoantimycins D and E) linked to a 1,4-disubstituted benzene ring via an imino group. Initial toxicity tests of 1-6 in MCF7 human breast cancer cells revealed that compounds 5 and 6 possess weak cytotoxic activity. Further structure-activity relationship analysis suggested the importance of the NH2 group at C-34 in 5 and 6 for cytotoxicity in MCF7 cells.