Sulphur amino‐acid degradation in subjects with hereditary glutathione synthetase deficiency (5‐oxoprolinuria)

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Abstract
The role of a low intracellular glutathione concentration in sulphur amino-acid degradation was investigated in two sisters (10 and 13 years old) with glutathione-synthetase deficiency, by determination of the urinary excretion of sulphur amino-acids and their main degradation products. The urinary excretion of total sulphur and inorganic sulphate was normal, indicating adequate dietary intake of sulphur amino-acids and normal oxidation to inorganic sulfate. Decreased excretion of N-acetylcysteine was found in the younger sister, which could be due to a reduced intracellular availabiliity of cyst(e)ine. Increased excretion of mercaptolactate was found in the older sister, probably featuring a more catabolic condition in this subject. She also had an increased excretion of thiosulphate. Low excretion of thiocyanate was observed in both subjects, probably a consequence of a reduced dietary intake of thiocyanate or its precursors. Neither glutathione nor .gamma.-glutamylcysteine were detectable in urine. The excretion of cysteinylglycine was clearly reduced, reflecting that this dipeptide mainly is a degradation product of glutathione.