Elsevier

Metabolism

Volume 38, Issue 6, June 1989, Pages 577-582
Metabolism

Cystathionine-synthase-deficient patients do not use the transamination pathway of methionine to reduce hypermethioninemia and homocystinemia

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Abstract

Methionine is supposed to be degraded via two known routes, the transsulfuration and the transamination pathways. In particular, patients with hypermethioninemia, due to a defect in the transsulfuration pathway, may catabolize significant amounts of methionine via the transamination pathway. In this study the relative amount of methionine degraded via the transamination pathway in 17 patients with homozygous homocystinuria, due to cystathionine synthase deficiency, was compared with 23 normal subjects, and with a patient with hypermethioninemia due to a deficiency in methionine adenosyltransferase. The homocystinuric patients and the normal subjects were studied in the fasting state as well as after methionine loading (0.1 g/kg body weight). It is concluded that in cystathionine synthase deficient patients, the transamination pathway is not quantitatively important in methionine degradation despite elevated methionine levels. This is in contrast to the patient with methionine adenosyltransferase deficiency, who catabolizes at least 20% of his dietary methionine via the transamination pathway.

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    Citation Excerpt :

    Consequently, those cells that lack transsulfuration will have some capacity for dealing with excess methionine. Methionine and Hcy levels could conceivably be reduced by the transamination of methionine but previous work has concluded that this is not a significant mechanism in HCU [32]. Hcy and methionine can be extruded into the extracellular space where they end up in the circulation and are subsequently excreted in the urine.

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This study was supported by a grant from the Netherlands Organization for Scientific Research (Medigon, NWO).

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