Proline catabolism

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

Vilchez S, L Moloina, C Ramos, JL Ramos (2000) Proline catabolism by Pseudomonas putida cloning, characterization, and expression of the put genes in the presence of root exudates. J Bacteriol 182 91-99. 

FIGURE 8.9 Arginine and proline catabolism. Glutamate-Y-semialdehyde, an intermediate in the pathways of arginine and proline breakdown, received its name because its structure consists of glutamate, but with the y-carboxyl group reduced to the aldehyde form. 

Proline. Proline catabolism begins with an oxidation reaction that produces A -pyrroline. The latter molecule is converted to glutamate-y-semialdehyde by a hydration reaction. Glutamate is then formed by another oxidation reaction. 

Proline catabolism follows the pathway shown in Fig. 5.1. When trypanosomatid utilize proline, products other than CO2 are formed indicating that the TCA cycle i... 

Removal of a-amino nitrogen by transamination (see Figure 28-3) is the first catabolic reaction of amino acids except in the case of proline, hydroxyproline, threonine, and lysine. The residual hydrocarbon skeleton is then degraded to amphibolic intermediates as outhned in Figure 30-1. 

There is no associated impairment of hydroxyprohne catabolism. The metabolic block in type II hyperpro-linemia is at glutamate-7-semiaIdeliyde dehydrogenase, which also functions in hydroxyprohne catabolism. Both proline and hydroxyprohne catabohsm thus are affected and A -pyrroline-3-hydroxy-5-carboxylate (see Figure 30-10) is excreted. 

Figure 30-3. Top Catabolism of proline. Numerals indicate sites of the metabolic defects in type I and type II hyper-prolinemias. Bottom Catabolism of arginine. Glutamate-y-semialdehyde forms a-ketoglutarate as shown above. , site of the metabolic defect in hyperargininemia.

The best known catabolic pathways of nitrogenous compounds are those of arginine, proline, allantoin and 4-aminobutyrate (GABA) degradation. Each of these is inducible under specific conditions, and all are subject to nitrogen-catabo-lite repression (see [7,9] and section 6.3). 

An enzyme that catalyzes the reduction of A -piperidein-2-carboxylate to piperidine-2-car-boxylate (r-pipecolate) in the catabolism of o-lysine by Pseudomonas putida ATCC12633 is an NADPH-dependent representative of a large family of reductases that are distributed among bacteria and archaea (Muramatsu et al. 2005). It also catalyzes the reduction of A -pyrrolidine-2-carboxylate to L-proline. 

Muramatsu H, H Mihara, R Kakutani, M Yasuda, M Ueda, T Kurihara, N Esaki (2005) The putative malate/ lactate dehydrogenase from Pseudomonas putida is an NADPH-dependent ALpiperideine-2-carboxyl-ate/A -pyrroline-2-carboxylate reductase involved in the catabolism of L-lysine and D-proline. J Biol Chem 280 5329-5335. 

FIGURE 18-26 Catabolic pathways for arginine, histidine, glutamate, glutamine, and proline. These amino acids are converted to a-ketoglutarate. The numbered steps in the histidine pathway are catalyzed by histidine ammonia lyase, urocanate hydratase, imida-zolonepropionase, and glutamate formimino transferase. 

Arginine and histidine contain five adjacent carbons and a sixth carbon attached through a nitrogen atom. The catabolic conversion of these amino acids to glutamate is therefore slightly more complex than the path from proline or glutamine (Fig. 18-26). Arginine is... 

C. S5mthesis and Catabolism of Proline, Ornithine, Arginine, and Polyamines... 

One route of catabolism of proline is essentially the reverse of its formation from glutamate. Proline oxidase yields A -pyrroline 5-carboxylate.145a,b... 

Biochemical Functions. Ascorbic acid has various biochemical fimctions, involving, for example, coUagen synthesis, immune fimction, drug metabohsm, folate metabolism, cholesterol catabolism, iron metabolism, and carnitine biosynthesis. Clear-cut evidence for its biochemical role is available only with respect to coUagen biosynthesis (hydroxylation of prolin and lysine). In addition, ascorbic acid can act as a reducing agent and as an effective antioxidant. Ascorbic acid also interferes with nitrosamine formation by reacting directly with nitrites, and consequently may potentially reduce cancer risk. 

Polysaccharides, 44, 58 Prokaryote Cell, 7 Proline, 439 Promoters, 391 Protamines, 149 Proteans, 151 Protein Biosynthesis, 448 Protein Catabolism, 428 Protein Maturation, 449 Proteins, 262 Purine Metabolism, 379 Purines, 113 Pyridoxine, 229 Pyrimidines, 113 Pyruvate Kinase, 288... 

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