Abstract
In vivo experiments of Ando, et al. and Tanaka, et al., in man have suggested that the metabolism of L-valine (val) to methylmalonate (mma) is via propionate (pro). In the present study, evidence has been gathered supporting this pathway from oxidation studies in cultured skin fibroblasts from normal individuals and patients affected with propionic acidemia and methylmalonic aciduria. Differentially labeled substrates (DL-val-2-C14, -4-C14; isobutyrate-l-C14, -2-C14) were incubated separately with intact cells. Volatile labeled C02 was determined and non-volatile organic acids were extracted and chromatographed. Nearly normal amounts of labeled C02 were liberated using val-2-C14 and isobutyrate-l-C14 by patients cells when compared to controls. Substantial amounts of a labeled non-volatile intermediate, presumably B-hydroxyisobutyric acid (B-hiba) were detected in all incubations. In the presence of methylene blue the amount of B-hiba was reduced with concomittant increase in CO2 production. These findings support that the metabolism of val to mma is via the intermediates of B-hiba, methylmalonic acid semialdehyde (mas) and pro rather than through mas to mma directly.
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