Protein translocation across biological membranes: cost what it may

Protein translocation across biological membranes can expend a large portion of the total cellular metabolic energy. Although energy sources for this process have been well characterized, its total energy cost was unclear. Recently, this problem was addressed in the thylakoidal pH-dependent cpTat pathway. It was estimated that approximately 3% of the total energy output of the chloroplast is used by this pathway.