Channel Active Mammalian Porin, Purified from Crude Membrane Fractions of Human B Lymphocytes and Bovine Skeletal Muscle, Reversibly Binds Adenosine Triphosphate (ATP)

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Abstract
A new aspect of mammalian porin (mammalian VDAC = mammalian voltage-dependent anion channel) is presented: channel active VDAC binds adenosine triphosphate (ATP) in the absence of Ca2+. Channel active "Porin 31HL" or "Porin 31BM", enriched from crude membranes of human B lymphocytes or whole cell lysates of bovine skeletal muscle, respectively, was bound to a nine atoms spacer ATP-agarose at pH 7.4 or 5.0 and reeluted from the resin by 10 mM ATP disodium salt. Furthermore, channel active "Porin 31BM" was labelled by [32P]ATP in a 1:1 stoichiometric relation. Binding of ATP to human porin was confirmed by studying the interaction of the synthetic porin fragment Type-1/Ac-35, comprising the putative nucleotide binding site G Y G F G, with trinitrophenyl-ATP (TNT-ATP) by scanning fluorometry. Peptide/TNP-ATP complexes clearly show enhancement of fluorescence intensity and a spectral shift of the fluorescence maximum. In a control experiment, using a porin fragment lacking the putative nucleotide binding site, no change of fluorescence emission was observed. Further confirmation for ATP binding by human VDAC arose from an autoradiographic experimental approach: the porin fragment Type-1/Ac-35 could be labelled by [32P]ATP, while a second porin fragment ending immediately before the putative nucleotide binding site could not; nor could a synthetic non porin peptide.