Syntheses and NMR Studies of Specifically Labeled Phosphocreatine, Creatinine, and Related 15N-Labeled Compounds

Article abstract of DOI:10.1021/ja00248a040

<2-15N>Creatine, <2-15N>creatinine, <2/3-15N>creatinine, <2-15N>phosphocreatinine, <2/3-15N>phosphocreatinine, <2-15N>phosphocreatine, and <2/3-15N>phosphocreatine have been synthesized. 1H and 15N NMR analyses of the labeled creatinines have established that creatinine is protonated at low pH exclusively at the unmethylated ring nitrogen (N-3) and indicate that in the predominant resonance from at low pH, conjugation to the carbonyl is present. 31P and 15N NMR analyses of the labeled phosphocreatinines establish that the site of phosphorylation of phosphocreatinine is on the exocyclic nitrogen.The 31P-15N one-bond coupling constant in <2-15N>phosphocreatine is 18 Hz, not 3 Hz as reported for doubly 15N-labeled phosphocreatine by Brindle et al.< Brindle, K.M.; Porteus, R:; Radda, G.K.Biochem.Biophys.Acta 1984, 786, 18>.Finally, 31P and 15N NMR analyses indicated that no spontaneous 15N/14N-positional isotope exchange occurs in specifically labeled phosphocreatine.The relatively large J_31p-15N value and the lack of chemical scrambling are prerequisites for the use of <2-15N>phosphocreatine in positional isotope exchange studies in enzymatic reactions.