In vitro complex formation between the octamer of mitochondrial creatine kinase and porin

An interaction of mitochondrial creatine kinase with purified outer mitochondrial porin (voltage-dependent anion channel) was shown by co-sedimentation assays as well as by gel permeation chromatography. Porin formed high M(r) complexes with wild-type mitochondrial creatine kinase as well as with an N-terminal deletion mutant, lacking the first five N-terminal amino acids. The complexes were identified by creatine kinase activity in parallel with immunoblotting using specific antibodies against the two proteins. In addition, porin induced octamerization of the N-terminal creatine kinase mutant, which under the same conditions without porin, did not polymerize but remained more than 90% dimeric. Furthermore, binding of mitochondrial creatine kinase to porin affected the conductance of porin when reconstituted in "black membranes." At 10 mV the pore in the complex adopted a low conductance (1.5-2 nanosiemens) state, compared to the high conductance state (3-4 nanosiemens) of the free incorporated pores. The former state of the pore is known to be cationically selective. Thus, besides a specific structural interaction, a defined physiological function is assumed of the mitochondrial creatine kinase-porin complexes that are discussed here.