IN living systems a transfer of amino groups occurs between certain amino-acids and keto-acids. This important reversible process, known as ‘transamination’1, effects a link between carbohydrate and protein metabolism, and the responsible enzymes, the transaminases, are activated by pyridoxal2 or pyridoxamine phosphates3. The proposed mechanisms of the reaction involve participation of a Schiff base between amino- and keto-acids4 or between amino-acids and pyridoxal phosphate5. Prototropic rearrangement followed by hydrolysis gives, respectively, the keto- and amino-acids or the keto-acid and pyridoxamine phosphate, the latter then undergoing a reverse reaction with a different keto-acid. A reversible, non-enzymic reaction between pyridoxal and amino-acids to give pyridoxamine and keto-acids, discovered by Snell6, was shown recently to be catalysed by trace metals (copper, iron, aluminium)7. Interest in this chemical process lies mainly in its possible connexion with the biological one ; therefore an explanation of the part played by metals in such reactions is clearly desirable.