Mitochondrial creatine kinase S-type (CKMT2, 57- fold) and U-type (CKMT1A, 18-fold) are responsible for the energy and metabolite transfer between mitochondria and cytoplasm (i.e. the creatine phosphate shuttle), and were increased in renal oncocytomas. The gene discussed is CKMT2; the disease is kidney oncocytoma.