Metabolic Fate of Sarcosyl-14C-glycine in Normal Young Rats

The metabolic fate of the non-physiological synthetic dipeptide, sarcosyl-2-¹⁴C]glycine, was investigated in normal young rats in vivo and in vitro compared to that of seryl-2-¹⁴C]glycine as a typical example of common physiological dipeptides. The radioactive dipeptides were synthesized from sarcosine or L-serine and 2-¹⁴C]glycine in our laboratory. When radioactive sarcosylglycine was given intraperitoneally, about 30% of the dose was excreted in the urine, and more than 90% of the urinary radioactivity was present in the sarcosylglycine fraction. The recovery of radioactivity in the the expired carbon dioxide and body protein was 8 and 50% of the dose, respectively, during a 24-h period. When the labeled serylglycine was given, the recovery of radioactivity in the urine was 8% of the dose, and 15% in the expired carbon dioxide. In slices of the kidney, liver and small intestine from normal rats, serylglycine was rapidly and almost completely hydrolyzed, and a large amount of free glycine was released. However, sarcosylglycine was hardly hydrolyzed to the corresponding amino acids in the liver and small intestine, and only slightly in the kidney. These results suggest that a considerable amount of sarcosylglycine given intraperitoneally was rapidly excreted into the urine of normal young rats, reflecting less sensitivity to hydrolysis by tissue peptidase(s) when compared to serylglycine.