Changes in the free amino acids of Spirodela polyrhiza (L.) Schleiden during growth inhibition by L-valine, L-isoleucine, or L-leucine. A gas chromatographic study

By means of gas-liquid chromatography the contents of free amino acids of the duckweed Spirodela polyrhiza have been determined after growth inhibition by L-valine, L-isoleucine and L-leucine. The most remarkable changes were when growth was inhibited with (1) valine; accumulation of a-aminobutyric acid, decrease in the isoleucine content and increase in that of leucine, (2) isoleucine: decrease in the leucine content and increase in that of valine, (3) leucine: decrease in both the valine content and isoleucine content. It is concluded that valine inhibits isoleucine synthesis by blocking acetohydroxy acid synthetase, isoleucine inhibits leucine synthesis, and leucine inhibits a common enzymatic step of the valine-isoleucine pathway.