Transport of proteins into chloroplasts

Abstract

The precursor of the small subunit of ribulose bisphosphate carboxylase in Pisum sativum (relative molecular mass 20000) is processed to the mature size (relative molecular mass 14000) by the purified processing enzyme in two steps. The maturation proceeds via an intermediate of M_r18000. Both processing reactions may be carried out by the same enzyme although different residues are involved in the two cleavage sites. The second cleavage is inhibited if the precursor is pre‐incubated with iodoacetate. The processing intermediate cannot be detected during the uptake of the precursor by intact isolated chloroplasts but iodoacetate‐treated precursor is taken up and converted to a number of polypeptides of M_r 18000 and below.