Catalytically active inclusion bodies (CatIBs) produced in E. coli are an interesting but currently underexplored strategy for enzyme immobilization. They can be purified easily and used directly as stable and reusable heterogenous catalysts. However, very few examples of CatIBs that are naturally formed during heterologous expression have been reported so far. Previous studies have revealed that the adenosine 5'-monophosphate phosphorylase of Thermococcus kodakarensis (TkAMPpase) forms large soluble multimers with high thermal stability. Herein, we show that heat treatment of solubilized protein induces aggregation of active protein which phosphorolysis all natural 5’-mononucleotides. Additionally, inclusion bodies formed during the expression in E. coli were found to be similarly active with 2−6 folds higher specific activity compared to the heat-induced aggregates. Interestingly, differences in the substrate preference were observed. These results show that the recombinant thermostable TkAMPpase is one of rare examples of naturally formed CatIBs.