Target sites amino acid biosynthesis inhibiting

In considering the commercially successful herbicides known to be inhibitors of amino acid biosynthesis, three aspects will be considered the kinetic description of the inhibition, the molecular interactions involved, and the relevance of the proposed target site to the observed physiological effects. Because of the extensive body of research published on the shikimate pathway and the herbicide glyphosate, this example will be taken as a paradigm of the inhibitor-enzyme relationship. The other cases considered will be the branched-chain amino acid family, histidine biosynthesis, and glutamine synthetase. 

Glyphosate is phloem mobile and accumulates in accordance with source-sink relationships in meristematic areas of the treated plants. " The general physiological effects of glyphosate are consistent with its acting as a metabolic poison. Death is a slow process, requiring days or weeks much more rapid effects, within hours, can be demonstrated at the biochemical level. These effects can be explained if the turnover rates of specific proteins, and therefore sensitivity to amino acid synthesis inhibition, differ. Inhibition of phenolic biosynthesis and chlorophyll formation and effects on the levels of the phytohormone 3-indoleacetic acid have been considered as target sites but can be viewed as necessary consequences of the primary interference with aromatic amino acid biosynthesis. " ... 

Target site studies can identify new processes for inhibition, ideally unique to the pest, and sometimes give information about the molecular geometry of active sites. However, investigations of fundamentally new targets is still limited. The tendency is to re-fkie understanding of well known inhibitors, or to look at untapped enzymes in proven multi-step pathways such as amino acid or sterol biosynthesis. 

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