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M Colombini

Publications and source records attributed to M Colombini.

At least 91 records · Page 5Linked to original sources
PubMed1985

Voltage-dependent channels found in the membrane fraction of corn mitochondria.

Transmembrane channels have been found in the membrane fraction of corn (Zea mays W64AN) mitochondria that exhibit a remarkable resemblance to the voltage dependent anion-selective channels (VDAC) located in the outer membrane of animal (Rattus norvegicus), protist (Paramecium aurelia), and fungal (Neurospora crassa) mitochondria. The channels in corn were demonstrated to be essentially identical to VDAC channels in three characteristic properties: (a) single channel conductance magnitude, (b) weak anion selectivity, and (c) nature of voltage dependence. These findings led us to conclude that the channels present in corn mitochondria are VDAC channels. This discovery may have repercussions concerning the regulation and function of higher plant mitochondria, and the causation of higher plant excitability.

Journal Article↗
PubMed1984

A novel mechanism for voltage control of channel conductance.

Many channel-formers can exist in conformational states with varying degrees of conductance. When the difference in the energy level between states is voltage dependent the result is a voltage-dependent channel. This voltage-dependence is usually attributable to the movement of charges or alignment of dipoles associate with channel-former. This paper presents a simpler mechanism by which the energy difference can be voltage dependent without the need for charge movement or dipole alignment. The voltage dependent energy difference between the high and low conducting states can arise from a change in electrical potential at a fixed charge located on the walls lining the pore (or field at a dipole fixed within the pore) which occurs as a result of the conformational change. This mechanism takes advantage of structural features normally found in channel formers and local changes resulting from channel opening and closing to generate the energy difference needed for voltage-dependence.

Cell Membrane Permeability↗
PubMed1984

Evidence that the crystalline arrays in the outer membrane of Neurospora mitochondria are composed of the voltage-dependent channel protein.

Antibodies were raised in rabbits against the outer membrane of Neurospora mitochondria. Antibodies were obtained that were specific for this membrane's major polypeptide (Mr 31 000) and its slower-migrating derivatives on SDS-polyacrylamide gels. These antibodies inhibited the insertion into phospholipid bilayers of voltage-dependent ion channels from detergent extracts of the mitochondrial outer membranes. The same antibodies bound preferentially to membranes containing crystalline surface arrays in outer mitochondrial membrane fractions. These results indicate that the 31 kDa polypeptide is a component both of the ion channels and of the membrane arrays, suggesting identity between the functional and structural entities.

Antibody Specificity↗
PubMed1983

Purification of VDAC (voltage-dependent anion-selective channel) from rat liver mitochondria.

The outer membrane of rat liver mitochondria contains a channel-forming protein known as VDAC (voltage-dependent anion-selective channel). This protein has been functionally purified by a combination of ion exchange chromatography, gel filtration and affinity chromatography on a Concanavalin A-containing column. An estimated 300-fold purification was achieved over the specific activity in mitochondrial membranes. When the purified protein is run on an SDS polyacrylamide gel, essentially only one band is present at a position consistent with a molecular weight of 32,000. The resulting protein is functional and behaves normally based on channel size, selectivity and voltage dependence.

Animals↗
PubMed1983

Structural and functional evidence for multiple channel complexes in the outer membrane of Neurospora crassa mitochondria.

The outer membrane of mitochondria contains proteins that form channels called VDAC (voltage-dependent anion-selective channels). Two independent lines of evidence suggest that these channels occur in specific complexes in the outer membrane of Neurospora mitochondria. Electron microscopic images of these outer membranes reveal polymorphic crystalline arrays of putative pores. These arrays can be shown to be interrelated by movement in the membrane plane of a particular rigid channel triplet or of regular aggregates of this triplet. Detergent extracts of the same outer membranes induce single- and multiple-step conductances in planar phospholipid membranes, with a marked preference for the insertion of triplets and multiples of triplets. The tendency of the mitochondrial channels to occur as extended arrays, apparently built up from triplets, may have important functional and evolutionary implications.

Biological Transport↗
PubMed1981

A food dye, erythrosine B, increases membrane permeability to calcium and other ions.

A widely used food additive erythrosine B, which has been implicated in minimal brain dysfunction in children was examined for its ability to increase membrane permeability to calcium ions. Planar phospholipid bilayer membranes become permeable to calcium, potassium and chloride ions and when erythrosine B is added to the aqueous phase at concentrations which were used by others to demonstrate effects on neuromuscular preparations. The observed increase in permeability to Ca2+ was of sufficient magnitude that equivalent effects on cells would seriously tax the systems which maintain low cytoplasmic Ca2+ levels. The permeability increase in the lipid bilayer membrane is time dependent and increases with erythrosine B concentration raised to a high power (4 to 7). This indicates that the permeability pathway is generated by the cooperative action of a number of erythrosine molecules. This permeability increases dramatically with increasing transmembrane voltage indicating that cells or organelles bearing potentials across their membranes should be particularly sensitive to the dye. We propose that the neurological effects of erythrosine stem from the increased Ca2+ permeability.

Calcium↗
PubMed1981

Diphtheria toxin fragment forms large pores in phospholipid bilayer membranes.

The cytotoxic effect of diphtheria toxin requires the entry of its enzymatic A fragment (Mr approximately 21,000) into the cytosol of sensitive cells. We show that the B45 fragment (Mr approximately 24,000) forms, in lipid bilayers, pores that are large enough (diameter greater than or equal to 18 A) to allow the passage of extended fragment A. Pore formation is maximal when the B45-containing side is at low pH (4.7) and the opposite side is at high pH (7.4). These conditions resemble the pH gradient existing across lysosomal membranes. We suggest that fragment A passes through these pores from acidic endocytotic vesicles (lysosomes?) to the cytosol.

Conductometry↗
PubMed1980

Structure and mode of action of a voltage dependent anion-selective channel (VDAC) located in the outer mitochondrial membrane.

VDAC is a channel-forming protein, located in the outer mitochondrial membrane, whose properties are consistent with the known permeability behavior of that membrane. When extracted with Triton X-100, VDAC exists as a 110,000 molecular weight glycoprotein complex which is a prepackaged channel. When inserted into liposomes, the permeability increase to non-electrolytes is consistent with a pore radius of 20. In a planar lipid bilayer, VDAC is anion selective and voltage gatable. This suggests that the permeability pathway in the outer mitochondrial membrane might be under physiological control. Many of VDAC's properties are qualitatively very similar, although quantitatively different, to those of porin, the channel responsible for the permeability of the outer membrane of at least some gram negative bacteria.

Animals↗
PubMed1976

Reconstitution in planar lipid bilayers of a voltage-dependent anion-selective channel obtained from paramecium mitochondria.

We have incorporated into planar lipid bilayer membranes a voltage-dependent, anion-selective channel (VDAC) obtained from Paramecium aurelia. VDAC-containing membranes have the following properties: (1) The steady-state conductance of a many-channel membrane is maximal when the transmembrane potential is zero and decreases as a steep function of both positive and negative voltage. (2) The fraction of time that an individual channel stays open is strongly voltage dependent in a manner that parallels the voltage dependence of a many-channel membrane. (3) The conductance of the open channel is about 500 pmho in 0.1 to 1.0 M salt solutions and is ohmic. (4) The channel is about 7 times more permeable to Cl- than to K+ and is impermeable to Ca++. The procedure for obtaining VDAC; AND THE PROPERTIES OF THE CHANNEL ARE HIGHLY REPRODUCIBLE. VDAC activity was found, upon fractionation of the paramecium membranes, to come from the mitochondria. We note that the published data on mitochondrial Cl- permeability suggest that there may indeed be a voltage-dependent Cl- permeability in mitochondria. The method of incorporating VDAC into planar lipid bilayers may be generally useful for reconstituting biological transport systems in these membranes.

Animals↗