The cetonic pathway (I)

This paper presents the most evoluted biochemical pathway of transition fro nt the ternary to the quaternary metabolisme with respect to the a-aminoaci ds formation. The problem is presented from thee evolutionary perspective. The transamination process (i.e. the cetonic way) is presented in parallel with the Krebs cycle (of the tricarboxylic acids) in which its origin is pr esumed (at least at the level of the reactivity development). As an work hy pothesis is discussed the problem of the direct transamination (i.e. withou t a cosubstrate-a situation who can be associated with the begining conditi ons of this metabolisme). The structure of the transamination cosubstrate i s also discussed. The evolution of the biochemical reactivity is discussed from the evolutionary perspective.