Some metabolic studies of β-aminoisobutyric acid

DL-β-aminoisobutyric acid-β-14C was synthesized and administered intraperitoneally to rats. Radioactivity was incorporated into all vascular tissues. Maximum radioactivity was found in rat livers and kidneys within 30 minutes after injection. β-Aminoisobutyric acid-β-14C was readily converted to 14CO2. In two hours, about 20% of the injected dose appeared as 14CO2. Approximately 17% of the injected radioactivity was excreted in the urine in 24 hours. Fractionation of the urine by ion exchange chromatography revealed the presence of several radioactive peaks. Two peaks have been identified, one as unchanged β-aminoisobutyric acid and the other as N-acetyl-β-aminoisobutyric acid. When β-aminoisobutyric acid-β-14C together with an overload of succinate was given intraperitoneally to rats, succinate-14C was isolated from the urine. Degradation of urinary-14C-succinate by the Schmidt reaction revealed the presence of about 80% of the 14C in the carboxyl carbons and 20% in the methylene carbons. When valine-4-14C and an overload of cold β-aminoisobutyric acid was given intraperitoneally to rats, β-aminoisobutyric acid-14C was isolated from the urine. These results indicate that succinate is an end produce of β-aminoisobutyric acid catabolism by the rat and that β-aminoisobutyric acid is in equilibrium with the pathway by which valine is metabolized.