Glyphosate as a probe of the pentafunctional arom protein of Euglena gracilis

Glyphosate (N-(phosphonomethyl)glycine) inhibited the growth of myxotrophically cultured Euglena gracilis. This inhibition was reversed by a combination of end products of the aromatic amino acid biosynthetic pathway, including the quantitatively minor vitamin precursors. This suggested a stringent inhibition of the early-pathway reactions, five consecutive reactions of which are catalyzed by the arom protein. Glyphosate was shown to affect the catalytic properties of the arom protein, thus providing a new means for studying the relationships of intrapathway catalytic sites to one another in this unique protein.