THE STRUCTURE OF MITOCHONDRIAL CREATINE-KINASE AND ITS MEMBRANE-BINDING PROPERTIES

The biochemical and biophysical characterization of the mitochondrial creatine kinase (Mi-CK) from chicken cardiac muscle is reviewed with e mphasis on the structure of the octameric oligomer by electron microsc opy and on its membrane binding properties. Information about shape, m olecular symmetry and dimensions of the Mi-CK octamer, as obtained by different sample preparation techniques in combination with image proc essing methods, are compared. The organization of the four dimeric sub units into the Mi-CK complex as apparent in the end-on projections is discussed and the consistently observed high binding affinity of the f our-fold symmetric end-on faces towards many support films and towards each other is outlined. A study on the oligomeric state of the enzyme in solution and in intact mitochondria, using chemical crosslinking r eagents, is presented together with the results of a search for a poss ible linkage of Mi-CK with the adenine nucleotide translocator (ANT). The nature of Mi-CK binding to model membranes, demonstrating that rat her the octameric than the dimeric subspecies is involved in lipid int eraction and membrane contact formation, is resumed and put into relat ion to our structural observations. The findings are discussed in ligh t of a possible in vivo function of the Mi-CK octamer bridging the gap between outer and inner mitochondrial membranes at the contact sites.