ATP Regeneration System Using <I>E. coli</I> ATP Synthase and <I>Gloeobacter</I> Rhodopsin and Its Stability

Abstract

Great efforts in using non-photosynthetic bacteria as light-utilizing bacteria for producing biomaterials have been developed recently as increasing interest in renewable resources such as light energy. With respect to producing bio-materials industrially such as food ingredients and amino acids, huge amount of adenosine-5'-triphosphate (ATP) is required. In this work, we developed a bio-ATP-synthesis system using ATP synthase of Escherichia coil as a biocatalyst and a microbial rhodopsin which is from primitive cyanobacteria, Gloeobacter violaceus. Gloeobacter rhodopsin (GR) is a light-driven proton pump. Besides electro-chemical gradient produced by cellular respiration system, GR produces a proton gradient using light illumination which is used in additional driving force of synthesizing ATP by ATP synthase. Inverted membrane vesicle was prepared so that it could be incorporated with both of GR and ATP synthase and produced ATP in the exterior side of the vesicle in the presence of light. Since inverted membrane vesicle does not contain precursors for ATP, we added ADP and inorganic phosphate (P(i)). Then, we measured the amounts of ATP produced by ATP synthase in the presence of light. As the average value of 6 samples, 4.79 x 10(-2) micromole of ATP produced for 1 microg of GR per minute. Also, we measured again after 7 days and 65 days, respectively, in order to check the stability of the bio-ATP-synthesis system. Amount of ATP produced decayed double-exponentially and an expected value of half-life of the system was 1.5 days and 39.7 days. Our results demonstrate that ATP was regenerated successfully by using GR and ATP synthase. However, the stability of ATP synthase should be increased to use this system industrially in the near future.