The occurrence of hsp70 in the outer membrane of plant mitochondria.

Hsp70 was localized to the mitochondrial outer membranes of bean and cauliflower mitochondria. Western blotting showed that the outer membrane hsp70 was antigenically distinct from the mitochondrial-matrix hsp70, but was similar to the cytosolic form. The protein was resistant to solubilization with 200 mM sodium carbonate which showed the hsp70 was tightly bound to the outer membrane. Proteinase K studies suggested that the hsp70 was partially exposed to the cytosol with approximately 17% of the protein protease-accessible. It is suggested that the position of the outer membrane hsp70 could relate to a precursor unfolding function during protein import into mitochondria.