Figure 6. Structural models of the human PPA1 active site with potential peptide substrates containing a phosphotyrosine and a phosphothreonine. A) A phosphotyrosine (p-Y185), within the context of a pentapeptide 182-MTpPYpV, is bound at the active site. B) A phosphothreonine (p-T183), within the context of a hexapeptide 181-MMTpPYpV, is bound at the active site. The phosphorylated peptides are rendered in stick mode and space-filling mode in the two panels of the figures.