The role of a disulfide bridge in the stability and folding kinetics of Arabidopsis thaliana cytochrome c6A

► Equilibrium and kinetic (un)folding of two cytochrome c6 proteins has been studied. ► The presence of a disulfide bond in cytochrome c6A influences the global stability. ► Stopped-flow kinetics reveal the formation of an on-pathway folding intermediate. ► The disulfide bond determines the structural properties of the folding intermediate.