Y semialdehyde

L-glutamic-y-semialdehyde) B.flavum L-Glutamine pro sulfite is effective 13.2 144... 

Proline. Prohne forms dehydroprohne, glutamate-y-semialdehyde, glutamate, and, ultimately, a-ketoglu-tarate (Figure 30—3, top). The metabohc block in type I kyperprolinemia is at proline dehydrogenase. 

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.

Baich, A. Vogel, H.J. N-Acetyl-y-glutamokinase and N-acetylglutamic y-semialdehyde dehydrogenase repressible enzymes of arginine synthesis in Escherichia coh. Biochem. Biophys. Res. Commun., 7, 491-496 (1962)... 

We have already described the biosynthesis of glutamate and glutamine. Proline is a cyclized derivative of glutamate (Fig. 22-10). In the first step of praline synthesis, ATP reacts with the y-carboxyl group of glutamate to form an acyl phosphate, which is reduced by NADPH or NADH to glutamate y-semialdehyde. This intermediate undergoes rapid spontaneous cyclization and is then reduced further to yield proline. 

In the conversion of the /V-acetyl-y-glutamyl phosphate to A-acetylglutamic-y-semialdehyde (fig. 22.2), two processes occur An elimination of a phosphate and a reduction. Which step occurs first Also can you propose a reason for the use of the phosphate group in the first place ... 

Ornithine Glutamic-y- semialdehyde Putrescine Putrescine is toxic and has the odor of putrid flesh... 

Glutamine is hydrolyzed to glutamate and NH4 + by glutaminase. Proline and arginine are each converted into glutamate y-semialdehyde, which is then oxidized to glutamate (Figure 23.25). 

Glutamic y-semialdehyde cyclizes with a loss of H2O in a nonenzymatic process to give A i-pyrroline-5-carboxylate, which is reduced by NADPH to proline. Alternatively, the semialdehyde can be transaminated to ornithine, which is converted in several steps into arginine (Section 23.4.1). 

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. 

All of the amino acids except lysine, threonine, proline, and hydroxyproline participate in transamination reactions. Transaminases exist for histidine, serine, phenylalanine, and methionine, but the major pathways of their metabolism do not involve transamination. Transamination of an amino group not at the a-position can also occur. Thus, transfer of 3-amino group of ornithine to a-ketoglutarate converts ornithine to glutamate-y-semialdehyde. 

The urea so formed is distributed throughout the body water and excreted. The renal clearance of urea is less than the glomerular filtration rate because of passive tubular back-diffusion. Diffusion of urea in the intestine leads to formation of ammonia, which enters the portal blood and is converted to urea in liver. Reentry of ornithine into mitochondria initiates the next revolution of the urea cycle. Ornithine can be converted to glutamate-y-semialdehyde (which is in equilibrium with its cyclic form A -pyrroline-5-carboxylate) by ornithine aminotransferase and de-carboxylated to putrescine by ornithine decarboxylase. Ornithine is also produced in the arginine-glycine trans-amidinase reaction. 

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. 

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