Phosphocreatine in Ehrlich ascites tumor cells detected by noninvasive 31P NMR spectroscopy

³¹P NMR spectra of intact Ehrlich ascites tumor cells of high phosphorylation potential reveal a well-defined resonance peak assignable to phosphocreatine, corresponding to 2.3 μmoles/ml cell H₂O in adenosine-treated cells containing 5.2 μmoles ATP/ml. The NMR spectrum of Ehrlich cells incubated with iodoacetate and glucose indicates depletion of phosphocreatine and ATP to undetectable levels and substantial accumulation of fructose-1,6-bisphosphate. From the difference between the chemical shifts of internal P_i and phosphocreatine resonances, the intracellular pH was estimated to be 7.1 ± 0.1 in protein-synthesizing cells suspended in a medium of pH 7.4 at 10°C. Ehrlich cells are unable to transfer the labeled amidine group from L-(guanidino-¹⁴C)-arginine to the large intracellular glycine pool to form labeled guanidinoacetate, the demethylated precursor of creatine. These results imply that the synthesis of phosphocreatine in ATP-rich Ehrlich cells is limited primarily by the extracellular free creatine supply, the extent of which depends upon the degree of cachectic perturbation of energy and nitrogen metabolism of the tumor-bearing host.