Intermediary metabolism of L-CYSTEINESULFINIC ACID (cas 1115-65-7) in animal tissues☆

Add time:08/15/2019    Source:sciencedirect.com

1.1. Homogenates and soluble extracts of rat liver mitochondrial acetone powder catalyze the rapid, coupled oxidation of cysteinesulfinate (CSA) and fumarate (or malate) to yield pyruvate, aspartate, and inorganic sulfate, as well as an analogous reaction between CSA and α-ketoglutarate to yield pyruvate, glutamate, and sulfate. In preparations from heart mitochondria the same reactions occur, except that the sulfur moiety of CSA accumulates as sulfite.2.2. The reactions above have been shown to involve rapid transaminations of CSA with α-ketoglutarate or oxalacetate. β-Sulfinylpyruvate, the product of these transaminations does not accumulate in the preparations but is cleaved to pyruvate and sulfite. The latter is oxidized to sulfate by sulfite oxidase in liver preparations but not by heart mitochondria.3.3. The very slow formation of oxalacetate from fumarate or malate by malic dehydrogenase in the mitochondrial system is greatly enhanced by the presence of CSA, by virtue of the rapid and complete removal of oxalacetate in the transamination reaction.4.4. Highly purified glutamic-oxalacetic transaminase catalyzes the reaction of CSA and α-ketoglutarate more rapidly than the transamination between aspartate and α-ketoglutarate. It is suggested that the observed transamination of CSA with oxalacetate and α-ketoglutarate may be the result of the action of glutamic-oxalacetic transaminase.5.5. Another, apparently non-transaminative, oxidation of CSA to pyruvate, sulfate, and ammonia has been observed in fresh rat liver mitochondrial acetone powders. The reaction is DPN-dependent. It is suggested that the initial steps may be the anaerobic dehydrogenation of CSA by a DPN-linked enzyme to β-sulfinylpyruvate and ammonia and that the further metabolism of the keto acid is identical with that occurring in the coupled reactions described.6.6. It is pointed out that these results and other data in the literature confirm the view that the mineralization of the sulfur moiety of cysteine in liver occurs at the oxidation level of CSA and entails cleavage of β-sulfinylpyruvate to sulfite, followed by the action of sulfite oxidase.7.7. The central position of transaminations involving CSA in the interrelations of carbohydrate and sulfur metabolism is discussed.

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