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Martin Klingenberg

Publications and source records attributed to Martin Klingenberg.

7 recordsLinked to original sources
PubMed2006

Transport catalysis.

Carrier linked solute transport through biomembranes is analysed with the viewpoint of catalysis. Different from enzymes, in carriers the unchanged substrate induces optimum fit in the transition state. The enhanced intrinsic binding energy pays for the energy required of the global conformation changes, thus decreasing the activation energy barrier. This "induced transition fit" (ITF) explains several phenomena of carrier transport, e.g., high or low affinity substrate requirements for unidirectional versus exchange, external energy requirement for "low affinity" transport, the existence of side specific inhibitors to ground states of the carrier, the requirement of external energy in active transport to supplement catalytic energy in addition to generate electrochemical gradients.

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PubMed2005

Ligand-protein interaction in biomembrane carriers. The induced transition fit of transport catalysis.

Carrier-linked transport through biomembranes is treated under the view of catalysis. As in enzymes, substrate-protein interaction yields catalytic energy in overcoming the activation barrier. At variance with enzymes, catalytic energy is concentrated on structural changes of the carrier rather than on the substrate destabilization for facilitating the global protein rearrangements during transport. A transition state is invoked in which the binding site assumes the best fit to the substrate, whereas in the two ground (internal and external) states, the fit is poor. The maximum binding energy released in the transition state provides catalytic energy to enable the large carrier protein transformations associated with transport. This "induced transition fit" (ITF) of carrier catalysis provides a framework of rules, concerning specificity, unidirectional versus exchange type transport, directing inhibitors to the ground state instead of the transition state, and excluding simultaneous chemical and transport catalysis (vectorial group translocation). The possible role of external energy sources (ATP and Deltapsi) in supplementing the catalytic energy is elucidated. The analysis of the structure-function relationship based on new carrier structures may be challenged to account for the workings of the ITF.

Binding Sites↗
PubMed2002

A large Ca2+-dependent channel formed by recombinant ADP/ATP carrier from Neurospora crassa resembles the mitochondrial permeability transition pore.

Strong support for the central role of the ADP/ATP carrier (AAC) in the mitochondrial permeability transition (mPT) is provided by the single-channel current measurements in patch-clamp experiments with the isolated reconstituted AAC. In previous work [Brustovetsky, N., and Klingenberg, M. (1996) Biochemistry 35, 8483-8488], this technique was applied to the AAC isolated from bovine heart mitochondria. Here we used recombinant AAC (rAAC) from Neurospora crassa expressed in E. coli, since AAC from mammalian sources cannot be expresssed in E. coli. The rAAC is free from residual mitochondrial components which might associate with the AAC in preparation from bovine heart. Ca(2+)-dependent channels with up to 600 pS are obtained, which are gated at >150 mV. The channel corresponds to a preferential matrix-outside orientation of rAAC in the patch membrane as shown with carboxyatractylate and a polar gating asymmetry. The channel is inhibited by ADP and bongkrekate, not by carboxyatractylate. Cyclophilin, isolated from Neurospora crassa, suppresses the gating, thus increasing conductivity at high positive voltage. Cyclosporin A abolishes the cyclophilin effect. ADP does not eliminate the cyclophilin effect but produces fast large-amplitude flickering of the channel without a stable decrease of the channel conductance. Also the pro-oxidant tert-butyl hydroperoxide reversibly suppresses voltage gating of the channel. The results show that the AAC can be a conducting component of the mPT pore, exhibiting similar characteristics as the mPT pore (response to Ca(2+), BKA, ADP), with a cyclophilin and pro-oxidant-sensitive gating at high voltage.

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