Crystalline mitochondrial inclusion bodies isolated from creatine depleted rat soleus muscle

Rats were fed a 2% guanidino propionic acid diet for up to 18 weeks to induce cellular creatine depletion by inhibition of creatine uptake by this creatine analogue. Ultrastructural analysis of creatine depleted tissues showed that mitochondrial intermembrane inclusion bodies appeared in all skeletal muscles analysed, after 11 weeks of feeding. Heart had relatively few even after 18 weeks of analogue feeding and none were evident in kidney, brain or liver. These structures were strongly immuno-positive for sarcomeric mitochondrial creatine kinase and upon removal from mitochondria, the inclusion bodies were shown to diffract to a resolution of 2.5 nm. Two-dimensional image analysis and three-dimensional reconstruction revealed arrays of creatine kinase octamers with additional components between the octameric structures. The same mitochondria had a 3-fold higher extractable specific creatine kinase activity than controls. Molecular mass gel filtration of inclusion body containing mitochondrial extracts from analogue fed rat solei revealed mitochondrial creatine kinase eluting as an aggregate of an apparent molecular mass > or = 2,000 kDa. Mitochondrial creatine kinase of control soleus mitochondrial extract eluted as an octamer, with a molecular mass of 340 kDa. Respiration measurements of control solei mitochondria displayed creatine mediated stimulation of oxidative phosphorylation that was absent in analogue-fed rat solei mitochondria. The latter also had 19% and 14% slower rates of state 4 and maximal state 3 respiration, respectively, than control mitochondria. These results indicate that mitochondrial creatine kinase co-crystallises with another component within the inter membrane space of select mitochondria in creatine depleted skeletal muscle, and is inactive in situ.