Higher homolog and N-ethyl analog of creatine as synthetic phosphagen precursors in brain, heart, and muscle, repressors of liver amidinotransferase, and substrates for creatine catabolic enzymes
Abstract
Tissues of chicks fed 5% N-methyl-3-guanidinopropionate (N-amidino-N-methyl-beta-alanine) for 12 days accumulated the following amounts of free plus phosphorylated derivatives as mumol/g, wet weight: brain, 5.5; heart, 7.3; leg muscle, 21.0; and breast muscle, 24.4. Since total creatine levels remained nearly the same in brain, N-methyl-3-guanidinopropionate-P provided brain with a supplemental reservoir of high energy phosphate. Tissues of rats fed 2% N-ethylguanidinoacetate (N-amidino-N-ethylglycine) accumulated large amounts of N-ethylguanidinoacetate-P, which has thermodynamic properties similar to creatine-P and is the kinetically most reactive synthetic phosphagen yet described. N-Ethylguanidinoacetate derivatives replaced creatine derivatives mole-for-mole, and the fraction of synthetic to total phosphagen after 19 days was 60% in heart, 54% in slow oxidative muscle, 42% in fast glycolytic muscles, and 22% in brain. N-Ethylguanidinoacetate served as a false end product co-repressor of liver arginine:glycine amidinotransferase levels in both chicks and chick embryos; N-methyl-3-guanidinopropionate and N-propylguanidinoacetate were relatively inactive. Creatinine amidohydrolase reversibly cyclized both N-ethylguanidinoacetate and N-propylguanidinoacetate with even lower Km values than for creatine derivatives, but it did not react significantly with N-methyl-3-guanidinopropionate, 3-guanidinopropionate, or 1-carboxy-methyl-2-imino-imidazolidine (cyclocreatine). Creatine…
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