Diaminopimelate pathway lysine synthesis

Meadow and Work 193) found that of labeled pyruvate and aspartate was incorporated into intracellular diaminopimelic acid and into lysine of E. coli. It is very curious, however, that these compounds did not label the extracellular diaminopimelic acid. On the other hand, the label of C -glucose and acetate-2-C was incorporated into all of the diaminopimelic acid. This result indicates an independent pathway of synthesis of extracellular diaminopimelic acid. This difference may be related to the fact that intracellular diaminopimelic add is formed during growth, while the concentration of lysine in the medium is sufficient to allow normal protein and cell-wall synthesis, whereas exttacdlular diaminopimelic acid is formed only after the lysine has been exhausted. 

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. 

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