Abstract: The invention relates to an in vitro cell-free expression system incorporating a novel inorganic polyphosphate-based energy regeneration system. In certain embodiments, the invention includes a cell-free expression system where the cellular energy source, ATP, is regenerated from inorganic polyphosphate using a dual enzyme system. In this embodiment, this dual enzyme system may include thermostable Adenosyl Kinase, and/or Polyphosphate Kinase enzymes.