The uptake of creatine by various tissues from a mouse bearing tumor cells.

The activity of guanidoacetate methyltransferase has been measured in various tissues of mice and tumor cells. The creatine levels in tumor cells are high, although guanidoacetate methyltransferase activity was not detected. To confirm these results, labeled creatine was synthesized by guanidoacetate and its methyltransferase in the presence of S-adenosyl-L-[methyl-3H]methionine, and administered to a mouse with or without tumor cells. High levels of the uptake of the creatine were observed in tumor cells, intestine, heart and muscle of the mouse injected with [3H]creatine into a tumor-bearing mouse. These organs, however, had no detectable activity of guanidoacetate methyltransferase. Labeled creatine phosphate in the tissue was less than 10% compared to total labeled creatine.