NEW ENZYMATIC CHANGES OF L-CYSTATHIONINE CATALYZED BY BOVINE TISSUE-EXTRACTS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 17  (1) , 107-111
Abstract
L-Cystathionine was used as substrate for enzyme systems prepared by heating bovine tissue extracts in the presence of pyruvate at 60.degree. C for 10 min. Analysis of the products indicated that the systems converted L-cystathionine into the cyclic ketimine from which was detected by its spectral properties and by chromatography on the amino acid analyzer. Al, .alpha.-amino-butyrate and cystine were also produced. Pyruvate and .alpha.-ketobutyrate enhance the production of the ketimine by liver, kidney and heart extracts and are necessary for the brain extracts. .alpha.-Ketoglutarate is much less effective. Its presence favors the production of homocystine by all the extracts. Homocystine was found in the brain incubates when any of the ketoacids assayed were added. The overall reaction is explained by the action of heat stable cystathionine .gamma.-lyase and .beta.-synthase which produce .alpha.-ketobutyrate and pyruvate used for the transamination of the remaining cystathionine to the monoketoacid. This last compound cyclizes spontaneously into the ketimine form thus avoiding the removal of the 2nd amino group. This represents a new nontransulfurative path leading to the production of a 7 membered etherocyclic product whose biochemical implications are yet unexplored.