Description
The end product of the creatine-creatine phosphate energy shuttle; formed by the spontaneous and non-enzymatic cyclization of creatine, as well as from creatine phosphate via a phosphorylcreatinine intermediate, in skeletal muscle and brain; increased in the urine after exercise in mice and in the plasma of rats fed a high-protein diet for 20 months; serum creatinine levels have been used to estimate the GFR and as a marker of renal dysfunction