PROTON COUPLING IS PRESERVED IN MEMBRANE-BOUND CHLOROPLAST ATPASE ACTIVATED BY HIGH-CONCENTRATIONS OF TENTOXIN

The effect of tentoxin at high concentrations was investigated in thyl akoids and proteoliposomes containing bacteriorhodopsin and CF0CF1. Ve nturicidin-sensitive ATP hydrolysis, ATP-generated Delta pH and ATP sy nthesis were practically 100% inhibited at 2 mu M tentoxin, and restor ed to various extents beyond 50 <3 mu M. With respect to the native en zyme, tentoxin-reactivated ATPase had the following properties: (i) a higher Delta pH requirement to synthetise ATP; (ii) a decreased futile proton flow through CF0CF1 (without ADP), which remains 100% blocked by ADP. It is concluded that despite its altered kinetic performances, tentoxin-modified CF0CF1 preserves its mechanism and remains a tightl y coupled proton pump.