Diaminopimelic decarboxylase and

Scheme XI. Possible geometry of PLP-substrate and PLP-product complexes in meso-diaminopimelate decarboxylase.

Diaminopimelate decarboxylase catalyzes the final step in lysine biosynthesis in bacteria. The epimerase catalyzes the interconversion of the ll- and meso isomers of diaminopimelate. Because these enzymes are absent in mammals, they are considered to be potential targets for antimicrobial agents. 

Alkaloid metabolism in lupine was proved by Wink and Hartmann to be associated with chloroplasts (34). A series of enzymes involved in the biosynthesis of lupine alkaloids were localized in chloroplasts isolated from leaves of Lupinus polyphylls and seedlings of L. albus by differential centrifugation. They proposed a pathway for the biosynthesis of lupanine via conversion of exogenous 17-oxosparteine to lupanine with intact chloroplasts. The biosynthetic pathway of lupinine was also studied by Wink and Hartmann (35). Two enzymes involved in the biosynthesis of alkaloids, namely, lysine decarboxylase and 17-oxosparteine synthetase, were found in the chloroplast stoma. The activities of the two enzymes were as low as one-thousandth that of diaminopimelate decarboxylase, an enzyme involved in the biosynthetic pathway from lysine to diaminopimelate. It was suggested that these differences are not caused by substrate availability (e,g., lysine concentration) as a critical factor in the synthesis of alkaloids. Feedback inhibition would play a major role in the regulation of amino acid biosynthesis but not in the control of alkaloid formation. 

Nevertheless, an exception to the general rule of retention has recently been discovered in the form of mcfo-a,e-diaminopimelate decarboxylase from Bacillus sphaerkus (259). This PLP-dependent enzyme, which catalyzes the final step in lysine biosynthesis, is the only known amino acid decarboxylase to operate on an a-carbon having the D-configuiation (264). Inversion of configuration was demonstrated for the enzyme from Bacillus sphaerkus by conducting the decarboxylation reaction in H20 solvent and isolating as product (6I7)-l-[6-2H]lysine [Eq. (50)] ... 

The stereochemistry of meso-a,e-diaminopimelate decarboxylase from a eukaryotic source (wheat germ) also involves inversion of configuration (260). As suggested by Floss and Vederas inversion might be comprehensible if the enzyme evolved from a preexisting L-amino acid decarboxylase in which the dispositions... 

The enzyme a,E-diaminopimelate decarboxylase (EC 4.1.1.20) decar-boxylates the (R) center of (25,6/ )-ffieso-diaminopimelic acid 262 to give lysine 257a (Scheme 69). When this reaction was conducted in and... 

Biosynthesis catabolism Lys is formed in plants and bacteria from meso-2,6- diaminopimelic acid by diaminopimelate decarboxylase (EC 4.1.1.20). The catabolism proceeds through eleven enzymatic steps to acetoacetic acid (acetyl-CoA). L. is a precursor of the cadaverines. Because of its two amino groups it has a cross-linking function in polypeptides such as collagen and elastin, see also 5-hydroxylysine. L. is used as a fodder additive. 

In organisms containing diaminopimelic acid both the meso- and the LL-forms (189) occur. The interconversion of the two forms can now be explained by the finding of a diaminopimelic acid racemase (190). The presence of the racemase strengthens the conclusion that diaminopimelic decarboxylase is specific for the meso compound. 

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