Fig. 2.
Metabolite exchange between the bacteriocyte (host cell) and intracellular bacterium Buchnera aphidicola. Insect-mediated terminal reaction in synthesis of branched chain amino acids (BCAs) from immediate precursors: (S)-3-methyl-2-oxopentanoate to isoleucine, 4-methyl-2-oxopentanoate to leucine and 2-oxoisovalerate to valine). The reaction catalyzed by BCAT is reversible (terminal reaction in BCA synthesis /first reaction in BCA degradation) such that, although BCAT functions in most animal tissues in the degradation of BCAs, it is recruited to the bacteriocyte to mediate the final reaction in BCA synthesis.