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Updated: Jul 20, 2026

Studying Protein Import into Chloroplasts Using Protoplasts
Published on: December 10, 2018
Early steps in mitochondrial protein import: receptor functions can be substituted by the membrane insertion activity
R A Stuart1, D W Nicholson, W Neupert
1Institut für Physiologische Chemie der Universität München, Federal Republic of Germany.
Abstract:
The process of insertion of precursor proteins into mitochondrial membranes was investigated using a hybrid protein (pSc1-c) that contains dual targeting information and, at the same time, membrane insertion activity. pSc1-c is composed of the matrix-targeting domain of the cytochrome c1 presequence joined to the amino terminus of apocytochrome c. It can be selectively imported along either a cytochrome c1 route into the mitochondrial matrix or via the cytochrome c route into the intermembrane space. In contrast to cytochrome c1, pSc1-c does not require the receptor system/GIP for entry into the matrix. The apocytochrome c in the pSc1-c fusion protein appears to exert its membrane insertion activity in such a manner that the matrix-targeting sequence gains direct access to the membrane potential-dependent step. These results attribute an essential function to the receptor system in facilitating the initial insertion of precursors into the mitochondrial membranes.
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