Figure 3

Purine biosynthetic pathway associated with the LCA. In red are all the steps associated with the LCA. In white is the semienzymatic pathway associated with an early stage of cell development, previously proposed by Becerra et al.[10]. The proposed ancestral histidine biosynthesis that feeds AICAR is displayed in a box with bars. The substrates with prebiotic origins are shown in blue circles. Ribonucleotides that may have occurred in the LCA are in purple circles. The thiamine (vitamin B₁) metabolism is in gray. In dashed lines, is indicated the AICAR in backflow as a seed substrate to AIR.