Using quantum chemical methods, a team of researchers led by Dr. Matthias Granold and Professor Bernd Moosmann of the Institute of Pathobiochemistry at Johannes Gutenberg University Mainz solved one of the oldest puzzles of biochemistry. They uncovered why there are 20 amino acids that form the basis of all life today, even though the first 13 amino acids generated over time would have been sufficient to form a comprehensive repertoire of the required functional proteins. The decisive factor is the greater chemical reactivity of the newer amino acids rather than their spatial structure. In their publication in the leading journal PNAS, the Mainz-based researchers also postulate that it was the increase in oxygen in the biosphere that triggered the addition of supplementary amino acids to the protein tool box.