Diaminopimelate transamination and

A role for a-keto-c-aminopimelic acid on the pathway of lysine syntheds is indicated by the discovery of a transaminase that acts on both diaminopimelic acid and on lysine 194). Cell suspendons of acetone-dried bacteria at pH 5 were able to transaminate all three stereoisomers of diaminopimelic acid and also d- and L-lysine in the presence of pyridoxal phosphate, with pyruvate, oxalacetate, and a-ketoglutarate serving as amino group acceptors. 

The biosynthesis of lysine in higher plants involves the formation of a, e-diaminopimelate from aspartate and pyruvate. Transamination of this intermediate to the diketo compound and reduction of one carboxyl group to an aldehyde function may produce a compound capable of cyclization via aldol condensation, i.e., the C4 -I- C3 pathway. ... 

Aspartate 4-semialdehyde, seen, for example, in Scheme 12.13, which provided a pathway for the biosynthesis of the essential amino acid methionine (Met, M) and in Scheme 12.14, which holds a representation of the biosynthesis of threonine (Thr, T), is also a place to begin to describe a pathway to lysine (Lys, K). As shown in Scheme 12.19, aspartate 4-semialdehyde undergoes an aldol-type reaction with pyruvate (CHsCOCO ") in the presence of dihydropicoUnate synthase (EC 4.2.1.52) to produce a series of intermediates that, it is presumed, lead to (5)-23-dihydropyridine-2,6-dicarboxylate. Then, dihydrodipicolinate reductase (EC 1.3.1.26) working with NADPH produces the tetrahydropyridine, (S)-2,3,4,5-tetrahydropyridine-2,6-dicarboxylate.This heterocycle, in the presence of glutamate (Glu, E) and water, is capable of transamination directly to 2-oxoglutarate and (2S, 6S)-2,3-diaminopimelate in the presence of LL-diaminopimelate aminotransferase (EC 2.6.1.83), while the latter, in the presence of the pyridoxal dependent racemase... 

The occurrence of iV -succinyl-a-amino- -ketopimelio acid and its transamination to succinyl-L-diaminopimelic acid has also been reported 196). The transaminase has been purified about 150-fold chiefly by means of chromatography on DEAE-cellulose. This transaminase was shown to be distinct from several other transaminases present in E. coli. The purified enzyme was specific for glutamate as an amino group donor in the formation of succinyldiaminopimelic acid. Succinyl-meso-diaminopimelic acid was inactive as a substrate. 

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