Waegemann, Karin; Soll, Jürgen
Characterization of the protein import apparatus in isolated outer envelopes of chloroplasts.
In: The Plant Journal, Vol. 1, Nr. 2: S. 149-158
Isolated outer envelope membrane from pea (Pisum
sativum L.) chloroplasts can be used in vitro to study
binding and partial translocation of precursor proteins
destined for the inside of the organelle. Efficient binding
to a receptor protein on the outside of the membrane
vesicle and generation of a translocation intermediate
depends strictly on the presence of ATP. Protease
treatment of the translocation intermediate demonstrates
its insertion into the membrane. The membraneinserted
precursor protein cannot be extracted by 1 M
NaCl and is also NaOH resistant to a large extent. Mild
solubilization of outer envelope membranes by detergent
resulted in the isolation of a complex which still
contained the precursor protein. We have identified a
constitutively expressed homologue hsc 70 as part of
this membrane complex. Antibodies against hsp 70
(inducible heat shock protein 70) were able to immunoprecipitate
the complex bound precursor protein.
A second protein of 86 kDa molecular weight (OEP 86)
from the outer envelope membrane was also identified
as a major component of this complex.