In vivo D-ethionine inversion and its inhibition.

The quantitative study of the inversion of D-ethionine into L-ethionine in vivo, measured in the liver of rats by the formation of S-adenosylethionine from L-ethionine, demonstrates high efficiency of this conversion when lower doses of D-ethionine are used. At higher doses (> 25 mg (80 mumol)/100 g body wt) the accumulation of S-adenosylethionine is retarded. It is suggested that this decrease of S-adenosylethionine formation is due to an unknown as yet effect of D-ethionine on the L-ethionine metabolism. At these higher doses, the alternative assay of the inversion, based on determining the dilution of radioactive L-ethionine probes by inverted D-ethionine, demonstrates considerably higher inversion, supporting the previous assumption. The inversion can be inhibited by administering D-ethionine simultaneously with either kojic acid or sodium benzoate, both inhibitors of D-amino acid oxidase. Sodium benzoate administration is tolerated very well by rats and therefore may be used in chronic experiments.