Intramolecular isomerization from 1-pHis to 3-pHis is not described in the model as it is known not to occur. In contrast, intermolecular phosphoryl transfer is known to occur. But, we assumed that the hydrolysis of 1-pHis is faster than the transfer to another histidine and thus do not describe the transfer. We determined the half-lives of the phosphorylated species from the fitted rate constants that could not be determined empirically. In line with the literature, it became clear that any phosphate group at the 1-pHis position was most labile, with a half-life of 1.79 hours and 1.88 hours for 1-pHis and 1,3-bpHis, respectively. In contrast, 3-pHis was less labile, with a half-life of 10.6 ± 0.7 hours and 2.88 hours for 1,3-bpHis. The activation rate constants for the different nitrogen atoms in the histidine were in the same range. Taken together, the MAP is catalytically converted by histidine, resulting in multiple transiently phosphorylated species. 3-pHis is the most long-lived, so its observed yield is the highest. We embedded histidine in a peptide sequence and tested its reactivity to couple the reaction cycle to function in the future, for example, for producing self-sustaining protocells (vide infra) or for forming non-equilibrium self-assemblies. The most straightforward peptide design was placing the histidine between two glycines (G) and acetylating the NH2-terminus (Ac-GHG-OH, Fig. ). We added MAP to 75 mM Ac-GHG-OH under the same conditions as above and monitored the concentration profiles with 31 P-NMR over 90 hours. Ac-G(3-pH)G-OH appeared first, followed by Ac-G(1-pH)G-OH, whereas in contrast to His, the bisphosphorylated species was not observed (Fig. ).