Abstract
In photosynthetic organisms, the ATP synthase (FoF1) has several specific regulation systems to control the activity in response to daily light-dark cycles. The epsilon subunit of the chloroplast and cyanobacterial FoF1, which is known to act as an intrinsic inhibitor, strongly inhibits the ATPase activity compared with bacterial counterpart. Furthermore, the gamma subunit of the chloroplast and cyanobacterial FoF1 has the inserted sequence in the molecule. Deletion of this region emerged the highly active ATPase activity.
In order to understand the physiological impact of the epsilon and gamma subunits, we prepared and characterized a strain containing the C-terminal-truncated epsilon subunit, a strain containing the gamma mutant which lacks the inserted sequence, and a strain containing those double mutations in the cyanobacterium Synechocystis sp. PCC 6803. Response of the change of intracellular ATP level in these mutant cells against the light-dark conditions was very different each other. Based on the phenotype analysis of these mutants, physiological roles of the epsilon and gamma subunits of cyanobacterial FoF1 especially in the dark conditions are discussed.
