[Creatine kinase isoenzymes--characterization and functions in cell]

Creatine kinase (CK, EC 2.7.3.2) is a key enzyme of cellular bioenergetics. The tissue-specific distribution, subcellular localization and function of CK isoenzymes in tissues and cells with high energy requirements, as well as the molecular structure of mitochondrial CK, point to an important physiological role of CK system for cellular energetics. The extensive studies about properties of mitochondrial creatine kinase isoforms gave a new perspective to create a functional model of CK isoforms action called "phosphocreatine shuttle". In this model the CK isoforms together with easily diffusible compounds like creatine and phosphocreatine, maintain a cellular energy buffer and intracellular energy transport system, where the "high-energy" phosphate is transferred between site of ATP synthesis and site of ATP utilization. Mt-CK octamer is able to bridge two mitochondrial membranes and interacts functionally with porin VDAC and ANT in cardiolipin vicinity. Mt-CK with its substrates also activates oxidative phosphorylation and effectively inhibits formation of mitochondrial permeability transition pore. Any destabilization of octamer structure would induce an apoptosis process.