Figure 2. Comparison of the models of reducing equivalents transport pathway across (A) inner membrane (IM) of Gram-negative bacteria and (B) the thylakoid membranes chloroplast. (A) Hypothetical model of transferring reducing equivalents across the IM that involves protein folding in the periplasm. This oxidative protein folding disulfide bond isomerization pathway in Gram-negative bacteria through the Dsb family. The protein is transported to the periplasm by SecYEG, which is oxidized by DsbA. Reduced DsbA then transfers reducing equivalents to DsbB in the IM. Reduced DsbB then transfer reducing equivalents to quinone. When the protein is mis-oxidized, Trx in the cytoplasm transfers reducing power to DsbD in the cytoplasmic membrane, which then transfers it to DsbC for proper folding. (B) Hypothetical model of reducing equivalents across the thylakoid membrane that may be involved in possible protein folding and enzyme activity within the lumen. Reducing equivalents from the stroma are transferred through CcdA and HCF 164, followed by reduced redox-regulated proteins in the lumen. LTO1 oxidizes redox-regulated proteins. The arrows indicate the flow of reducing equivalents, blue for reduction and pink for oxidation. (Note: Figure A was adapted from From Melissa E. Reardon-Robinson, and Hung Ton-That J. Bacteriol. (2016) 198:746-754; while Figure B was adapted from Frontiers in Plant Sci (2017) doi: 10.3389/fpls.2017.01313)