Kinetic analysis of translocation into isolated chloroplasts of the purified ferredoxin precursor

Time courses of the import into isolated chloroplasts of the purified ferredoxin precursor were measured at different protein concentrations. Analysis of the initial import rates indicates the presence of one saturable import system with an apparent Km value of approximately 100 nM and a Vmax corresponding to the uptake of approximately 2.5 x 10(4) precursor proteins per minute per chloroplast. We conclude that the in vitro observed activity of the chloroplast protein import machinery, functioning independently from cytosolic factors, would be enough to allow chloroplast development at physiological rate.