Proline, biosynthesis from glutamate

Vogel discovered an alternate pathway of ornithine biosynthesis from glutamic acid involving AT-acetylglutamate 114, 116). He has obtained evidence that this is the major pathway for ornithine formation in E. colt and Neurospora 127). The pathway shown in Fig. 5 is of minor importance for ornithine biosynthesis but is the major one for proline. These conclusions have been substantiated by isotope competition experiments 128). The steps in the acetylglutamate pathway is shown in Fig. 6. 

Figure 28-8. Biosynthesis of proline from glutamate by reversal of reactions of proline catabolism.

S ATP 4- L-glutamate <2, 4, 5> (<2> the enzyme catalyzes the first step in the pathway from glutamate to proline [2,3] <2> enzyme is involved in biosynthesis of proline [4] <4> enzyme form GKl is involved in biosynthesis of L-Pro, enzyme form GK 2 is involved in biosynthesis of glutamine and the function of enzyme form GK 3 has not been found [6] <4> enzyme GK 1 is the first enzyme of the proline biosynthetic pathway... 

Figure 24-9 Biosynthesis of glutamate, glutamine, proline, and lysine from 2-oxoglutarate.

FIGURE 20.13 Biosynthesis of arginine and proline from glutamate. The key step is a partial reduction of glutamate to the corresponding aldehyde. 

The metabolic pathways with P5C as the central intermediate (Fig. 2) were initially defined as a system for proline biosynthesis (1, 2, 5) and this physiologic endpoint has been emphasized by a number of investigators (65, 92, 123). In both prokaryotes (5) and eukaryotes (6, 93, 99) the inability to synthesize P5C results in proline auxotrophy. On the other hand if one of the pathways for P5C synthesis is present, i.e., from either ornithine or glutamate, normal growth occurs in proline-free medium (93J. Because of its strategic location in intermediary metabolism investigators have hypothesized that this metabolic system mediates... 

The nitrogen of the basic amino acids lysine, histidine and arginine is not derived from wort amino acids but possibly from ammonium ions. In these cases intracellular oxoglutarate is aminated with ammonia to produce glutamate for biosynthesis. The imino acid proline is synthesized, without... 

Fig. 2. L-Glutamic acid. Biosynthesis of L-ornithine and L-proline from L-glutamic acid.

---