SYNTHETIC ANALOGUES OF CREATINE-P AS RESERVOIRS OF HIGH-ENERGY PHOSPHATE WITH UNUSUAL KINETIC AND THERMODYNAMIC PROPERTIES IN MUSCLE, HEART, BRAIN, AND TUMOR CELLS; PRESERVATION OF MYOCARDIAL ADENOSINE-5'-TRIPHOSPHATE LEVELS DURING ISCHEMIA
ROBERTS, JEFFREY JACK
Doctor of Philosophy
Several analogues of creatine have been synthesized, characterized, and fed to animals, and the accumulation and utilization by tissues of their high energy phosphorylated derivatives have been studied. Chicks fed 1-carboxyethy1-2-iminoimidazolidine(homocyclocreatine) accumulated the extremely stable synthetic phosphagen, 1-carboxyethyl-2-imino-3-phosphonoimidazolidine (homocyclocreatine-P) in breast muscle (32 (mu)mol/g wet wt), heart (7 (mu)mol/g), and brain (2.4 (mu)mol/g). Homocyclocreatine-P reacted with creatine kinase (EC 22.214.171.124) to regenerate ATP up to 200,000-fold more slowly than creatine-P, and its Gibbs standard free energy of hydrolysis was approximately 2 kcal/mol lower than that of creatine-P. Muscle, heart, and brain of chicks and mice fed N-ethylguanidinoacetate accumulated N-ethylguanidinoacetate-P, which was found to be the most reactive known analogue of creatine-P, with a similar Gibbs standard free energy of hydrolysis. Mouse Ehrlich ascites tumor cells incubated in vitro accumulated up to 8 (mu)mol/g packed cells of N-ethylguanid-inoacetate-P, which was shown to be utilized for the regeneration of ATP more rapidly and completely than another coexisting synthetic phosphagen, 1-carboxymethyl-2-imino-3-phosphonoimidazolidine(cyclocreatine-P). Dietary N-ethylguanidinoacetate reduced the level of arginine:glycine amidinotransferase (EC 126.96.36.199), the first enzyme of creatine biosynthesis, in liver of chicks. On the basis of V(,max)/K(,m), N-ethylgunidinoacetate was more active than creatine as substrate for bacterial creatinine amidohydrolase (EC 188.8.131.52), and was cyclized to a greater extent than creatine. Hearts of rats fed cyclocreatine accumulated 12 (mu)mol/g of cyclocreatine-P, higher levels of glycogen, and during subsequent ischemia demonstrated a nearly 2-fold delay in development of rigor-contracture, prolonged glycolysis, and a marked delay in depletion of ATP levels. During ischemia cyclocreatine-P continued to be utilized for ATP regeneration long after creatine-P stores had been exhausted.