Dihydrodipicolinate synthase

A further flux control step within L-lysine synthesis is the aspartate semialdehyde branch point. The aldehyde is either used as a substrate for the homoserine dehydrogenase, or together with pyruvate as a substrate for the dihydrodipicolinate synthase (Fig. 10). Whereas the homoserine dehydrogenase is allosterically controlled in its catalytic activity by the L-threonine concentration... 

Shiio, I. (1990) Threonine production by dihydrodipicolinate synthase-defective mutants of Brevibacterium flavum. Biotechnol Adv., 8 (1), 97-103. 

Dihydrodipicolinate synthase 2 dihydrodipicolinate dehydrogenase 3 spontaneous reaction 4 succinylase 5 succinyldiaminopimelate aminotransferase 6 succinyldiaminopimelate de-succinylase 7 diaminopimelate epimerase 8 diaminopimelate decarboxylase... 

Dihydrodipicolinate synthase dapA Consume L-aspartyl semialdehyde to produce L-lysine... 

These characteristics of lysine production were combined to make strains that were much more efficient producers. In addition, the introduction of a leucine-requiring mutation also increases the amount of lysine, since in the mutant dihydrodipicolinate synthase is released from repression hy leucine. 

Fatty acid co-3 desaturase 2, acyl-acyl carrier protein thioesterase, diacylglycerol acyl-transferase, dihydrodipicolinate synthase, high-lysine protein, truncated cysteine synthase... 

Initially, the first and last enzymes of the lysine branch of the aspartate pathway illustrated in Fig. 1 were isolated from higher plants. The first enzyme, dihydrodipicolinate synthase (10), is sensitive to inhibition by the pathway product, lysine (Wallsgrove and Mazelis, 1981). Results obtained with extensively purified DHDP synthase from wheat suspension cultures indicate that lysine is a competitive inhibitor with respect to aspartate semialdehyde and a noncompetitive inhibitor with respect to pyruvate (Kumpaisal et ai, 1987). In vivo regulation of this enzyme by feedback inhibition is supported by the isolation of mutants which overproduce lysine and are characterized by a lysine-insensitive DHDP synthase (Negrutiu et ai, 1984). 

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