Showing papers on "Mitochondrial carrier published in 1987"

Patch-clamping of the inner mitochondrial membrane reveals a voltage-dependent ion channel.

Abstract: The prime function of mitochondria is to provide the cell with adenosine triphosphate (ATP). ATP synthesis is driven by the protonmotive force (delta p), which is generated and maintained across the inner mitochondrial membrane (IMM) by the activity of the respiratory chain. It is widely believed that the IMM is unlikely to contain ion channels like those present in the plasma membrane, because the high rates of ion transport characteristic of open channels would be expected to dissipate the delta p. Although the small size of the organelle has prevented the use of classical electrophysiological methods, the recent introduction of the patch-clamp technique, which allows currents to be recorded from very small cells, has enabled us to test this hypothesis. By patch-clamping the IMM, we have identified a slightly anion-selective channel, which is voltage-dependent and has a mean conductance of 107 pS in the presence of symmetrical 150 mM KCl.

Transport of proteins to the mitochondrial intermembrane space: the 'sorting' domain of the cytochrome c1 presequence is a stop-transfer sequence specific for the mitochondrial inner membrane.

Abstract: The presequence of yeast cytochrome c1 (an inner membrane protein protruding into the intermembrane space) contains a matrix-targeting domain and an intramitochondrial sorting domain. This presequence transports attached subunit IV of cytochrome c oxidase into the intermembrane space (van Loon et al. (1987) EMBO J., 6, 2433-2439). In order to determine how this fusion protein reaches the intermembrane space, we studied the kinetics of its import into isolated mitochondria or mitoplasts and its accumulation in the various submitochondrial compartments. The imported, uncleaved fusion precursor and a cleavage intermediate were bound to the inner membrane and were always exposed to the intermembrane space; they were never found at the matrix side of the inner membrane. In contrast, analogous import experiments with the authentic subunit IV precursor, or the precursor of the iron-sulphur protein of the cytochrome bc1 complex also an inner membrane protein exposed to the intermembrane space), readily showed that these precursors were initially transported across both mitochondrial membranes. We conclude that the intramitochondrial sorting domain within the cytochrome c1 presequence prevents transport of attached proteins across the inner, but not the outer membrane: it is a stop-transfer sequence for the inner membrane. Since the presequence of the iron-sulphur protein lacks such 'stop-transfer' domain, it acts by a different mechanism.

Independent mutations at the amino terminus of a protein act as surrogate signals for mitochondrial import.

Abstract: Intracellular delivery of the mitochondrial F1-ATPase beta-subunit precursor from the cytoplasm into the matrix of mitochondria is prevented by deletion of its mitochondrial import signal, a basic amphipathic alpha-helix at its amino terminus. Using a complementation assay, we have selected spontaneous mutations which restore the correct in vivo localization of the protein containing the import signal deletion. Analysis of these mutations revealed that different functional surrogate mitochondrial targeting signals formed within a narrow region of the extreme amino terminus of the import signal deleted beta-subunit. These modifications specifically replace different acidic residues with neutral or basic residues to generate a less acidic amphipathic helix within a region of the protein which is accessible for interaction with the membrane surface. The observations of this study confirm the requirement for amphipathicity as part of the mitochondrial import signal and suggest how mitochondrial targeting signals may have evolved within the extreme amino terminus of mitochondrial proteins.

[42] Isolation of the outer membrane of plant mitochondria

Abstract: Publisher Summary This chapter discusses the steps involved in applying the former technique to the isolation of outer membranes from mitochondria, with emphasis on the specific problems encountered with plant mitochondria. Mitochondrial fractions isolated from the plant tissue by differential centrifugation alone are generally contaminated with various nonmitochondrial membranes (microsomes, plastids, peroxisomes, etc.) The outer membranes of the plant (and fungal) mitochondria are more resistant to rupture by osmotic swelling than the liver membrane. An enzyme activity that appears to be common to all plant mitochondrial outer membranes is the rotenone- and antimycin A-insensitive NADH: cytochrome c oxidoreductase activity (EC 1.6.99.3), which is first described for the liver membrane. The protein, phospholipid mass ratio in outer membranes isolated from plant mitochondria is approximately two. In electron micrographs of negatively stained plant mitochondrial outer membranes, the membranes display disordered arrays of stain-accumulating subunits.

Structure and Biogenesis of the Plant Mitochondrial Inner Membrane

Abstract: Growth and differentiation in plants depends upon the integrated metabolism of, and provision of energy by, both mitochondria and chloroplasts. While in recent years considerable progress has been made in our understanding of the factors which regulate chloroplast biogenesis and function, comparable studies on mitochondria have received far less attention (for a review see 1). This is surprising given the many developmental transitions throughout the plant life cycle that are associated with, or are dependent upon, marked changes in mitochondrial number, structure and metabolism. A priority is therefore to gain an understanding of the role of the mitochondrion in meeting the changing energy requirements of the cell, and hence in determining plant yield and viability. In addition to the elucidation of metabolic pathways, and determination of important regulatory or limiting steps, there is a need to understand the factors regulating mitochondrial biogenesis. This will involve an understanding of how genetic, developmental and environmental factors regulate biogenesis and how this, in turn, influences plant development.

Transport of d-B-hydroxybutyrate across rat liver mitochondrial membranes

Abstract: 1. 1. d -β-hydroxybutyrate, a major ketone body, is produced or converted in mitochondria from various animal tissues. 2. 2. It is an easy permeate anion of the inner mitochondrial membrane. However, its translocation is not a passive diffusion process since it is inhibited by pyruvate transport inhibitors like α-cyanocinnamate and derivatives. 3. 3. This carrier mediated process is associated with proton movements. Besides, dicarboxylate anions strongly inhibit the penetration into mitochondria. 4. 4. This is in agreement with the existence of a second transport process related to the dicarboxylate carrier.