Figure 1. Increased intracellular creatine in Myl-R cells is due to uptake from cell media, and not de novo synthesis.

(A) Glycine and arginine are required for the biosynthesis of creatine in a two-part reaction. Myl and Myl-R cells were maintained in total growth medium with or without the addition of 2-¹³C-glycine for 5 days. (B) Analysis of ¹H NMR spectra of each cell extract revealed that there was no statistically significant difference in percent incorporation of labeled glycine in the cell extracts from Myl and Myl-R cells. Whereas satellite peaks from 2-¹³C-glycine were only observed in Myl-R cells incubated with heavy glycine, satellite peaks associated with creatine were not observed under these conditions. The data shown are representative of three independent experiments.