A photodetoxification mechanism of the cyanobacterial hepatotoxin microcystin-LR by ultraviolet irradiation.
When microcystin-LR was exposed to UV, three major nontoxic compounds were formed. These compounds were identified as [4(E),6(Z)-Adda5]- and [4(Z),6(E)-Adda5]microcystin-LR, which are geometrical isomers of the Adda [3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4(E),6(E)-decadienoic acid] moiety of microcystin-LR, and a novel compound, tricyclo-Adda [(2S,3S,1'R,3'S,4'S,5'R,6'R,7'R)-3-amino-5-(4',6'-dimethyl-3'-methoxy tricyclo[5.4.0.0(1',5')]undeca-8',10'-dien-6'-yl)-2-methy l-4(E)-pentenoic acid]-containing microcystin-LR ([tricyclo-Adda5]microcystin-LR), which was formed by [2 + 2] addition between the benzene ring and the double bond at position 6-7 of the Adda moiety of the microcystin. The geometrical isomers were formed reversibly, and their equilibrium constants were almost the same. [Tricyclo-Adda5]microcystin-LR was also formed reversibly and was decomposed under UV light. These results suggest that the breakdown of microcystin-LR by UV irradiation proceeds via [tricyclo-Adda5]microcystin-LR.
Kaya
K
K
Environmental Chemistry Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan. kayakuni@nies.go.jp
Sano
T
T
D000818:Animals; D000458:Cyanobacteria; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000528:radiation effects* / Q000633:toxicity; D009682:Magnetic Resonance Spectroscopy; D008387:Marine Toxins; D051379:Mice; D008807:Mice, Inbred BALB C; D052998:Microcystins; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000737:chemistry / Q000528:radiation effects* / Q000633:toxicity; D013237:Stereoisomerism; D014466:Ultraviolet Rays
D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; C057862:cyanoginosin LR