Abstract
Extract: Decreased activities of methionine-activating enzyme (ATP: L-methionine-S-adenosyl-transferanse, E.c. 2.5.1.6) (23 and 18 versus normal 86 nmoles product produced/mg soluble protein/h) and cystathionine synthetase [30] (28 and 6 versus normal of 98 nmoles product produced/mg soluble protein/h) in the presence of normal activity of cystathionase [30] (104 and 108 versus normal of 125 nmoles product produced/mg soluble protein/h) were demonstrated in the liver of two patients with so-called hereditary tyrosinemia. This decreased activity also was associated with documented deficiency of p-hydroxyphenylpyruvic acid oxidase, tyrosine transaminase, and phenylalanine hydroxylase with values of 3 and 1.2 versus normal of 60, 2.6 and 0.8 versus normal of 20, and 3.5 versus normal of 13.7 μmoles/g wet weight of liver/h, respectively (table II). In one patient, the biopsy was performed after the concentration of tyrosine in the plasma had been made normal (less than 1.0 mg/100 ml) for 3 months by dietary restriction (fig. 2). This patient has subsequently maintained normal concentrations of amino acids in the plasma on an ad libitum diet for 18 months. These findings give evidence that the abnormalities on the pathway of metabolism of methionine are independent of the abnormality in the metabolism of tyrosine and that the latter may be self-limiting in some cases (table I).
Speculation: These studies suggest that the hypertyrosinemia and the hypermethioninemia seen in so-called here-ditary tyrosinemia are each nonspecific manifestations of a phenotype as yet unidentified. Whether or not methionine accumulates in the plasma in the presence of these defects in the transsulfuration pathway is probably a function of an enlarged free amino acid pool in the liver when protein synthesis in that organ is reduced.
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Gaull, G., Rassin, D., Solomon, G. et al. Biochemical Observations on So-called Hereditary Tyrosinemia. Pediatr Res 4, 337–344 (1970). https://doi.org/10.1203/00006450-197007000-00004
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DOI: https://doi.org/10.1203/00006450-197007000-00004
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