Screening Marine Fungi for Inhibitors of the C 4 Plant Enzyme Pyruvate Phosphate Dikinase: Unguinol as a Potential Novel Herbicide Candidate

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Abstract
A total of 2,245 extracts, derived from 449 marine fungi cultivated in five types of media, were screened against the C 4 plant enzyme pyruvate phosphate dikinase (PPDK), a potential herbicide target. Extracts from several fungal isolates selectively inhibited PPDK. Bioassay-guided fractionation of one isolate led to the isolation of the known compound unguinol, which inhibited PPDK with a 50% inhibitory concentration of 42.3 ± 0.8 μM. Further kinetic analysis revealed that unguinol was a mixed noncompetitive inhibitor of PPDK with respect to the substrates pyruvate and ATP and an uncompetitive inhibitor of PPDK with respect to phosphate. Unguinol had deleterious effects on a model C 4 plant but no effect on a model C 3 plant. These results indicate that unguinol inhibits PPDK via a novel mechanism of action which also translates to an herbicidal effect on whole plants.

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