Formation of pipecolic acid from D-lysine through the anaerobic reaction catalyzed by D-amino acid oxidase

Interaction between 1,4-thiazine derivatives and D-amino-acid oxidase

Aminoethylcysteine-ketimine (2H-1,4-thiazine-5,6-dihydro-3-carboxylic acid) strongly inhibits D-amino-acid oxidase (D-amino-acid:oxygen oxidoreductase (deaminating), EC 1.4.3.3). The inhibition is purely competitive (Ki = 3.3 X 10(-7) M). Aminoethylcysteine-ketimine modifies the visible spectrum of the enzyme: the absorption maxima of bound FAD shift from 375-455 nm to 385-445 nm with a definite shoulder at 465 nm; the appearance of a large absorption band centered at 750 nm may be due to a charge-transfer complex formation. The dissociation constant for the aminoethylcysteine-ketimine-enzyme complex, calculated by a photometric procedure (4 X 10(-7) M), is in good agreement with kinetic data. The dicarboxylic analogue of this inhibitor (lanthionine-ketimine) is ineffective in D-amino-acid oxidase inhibition and does not produce any spectral modification of the enzyme. These results confirm structural requirements for D-amino-acid oxidase inhibitor reported by other researchers. Ketimine reduced forms (thiomorpholine-2-carboxylic acid and thiomorpholine-2,6-dicarboxylic acid) are chemically synthesized and checked as D-amino-acid oxidase substrates: only thiomorpholine-2-carboxylic acid is oxidized to aminoethylcysteine-ketimine (Km = 2 X 10(-4) M).

[The fate of alpha and epsilon lysine amino groups in rat liver in vitro (author's transl)]

The fate of alpha and epsilon lysine amino groups has been explored in rat liver homogenate by means of L-lysine labelled selectively in the two positions. alpha-15NH2 and epsilon-15NH2 are rapidly incorporated into the amino group of glutamic acid and it seems at first that both transaminations occur simultaneously. But the reversible transfer of the amino group between alpha-aminoadipic acid and glutamic acid, determined by means of labelled alpha-aminoadipic acid, proceeds swiftly, and the incorporation of alpha-15NH2 from the corresponding labelled lysine in glutamic acid may be easily explained by epsilon-transamination and saccharopine formation. The direct transamination of the alpha-amino group of L-lysine is most improbable and might be limited to some microorganisms and to epsilon-N-substituted lysine derivatives.