An example of substrate channeling between co-immobilized enzymes. Coupled activity of myosin ATPase and creatine kinase bound to frog heart myofilaments.

In myofilaments obtained by Triton X-100 lysis of frog heart cells in high ionic strength medium, the activity of bound creatine kinase cannot be detected by a coupled enzymatic assay. ATP is channelized toward myosin ATPase, through the unstirred layer near myofilaments and cannot diffuse into the bulk solution. Model systems based upon the coupled kinetics of enzymes co-immobilized on the same surface may explain this behaviour. This may also account for why myofilament-bound creatine kinase is more efficient than free enzyme in the cytosol for the physiological recycling of ADP into ATP.