Glutamate formation

Figure 29-5. The i-glutamate dehydrogenase reaction. NAD(P) means that either NAD or NADP can serve as co-substrate. The reaction is reversible but favors glutamate formation.

Partial inhibition of glycolysis by saturated fatty acids has been observed in Ehrlich ascites tumor cells. Palmitate and acetate decreased glutamate formation from glutamine (the first step in glutaminolysis) in this cell line, suggesting the possible role of fatty acids as an alternative energy source (Butler et al., 1999). 

Glutamate synthetase activity was determined by following glutamate formation. The reaction mixture contained in a final volume of 0.9 mL 45 //mol potassium phosphate buffer (pH 7.0), 5 /u.mol L-glutamine, 1 //mol 2-oxoglutarate, 5 //mol aminooxyacetate, 10 nmol Synechococcus ferredoxin, and enzyme. The reaction was started by adding 0.8 mg of sodium dithionite freshly dissolved in 0.1 mL of 0.12 M NaHCO and stopped after 15 minutes at 30°C by the addition of 0.6 mL of 1 N HQ. 

Figure 9.46 L-Glutamate formation with respect to incubation time at 37°C due to the glutaminase activity. (From Unnithan et al., 1984.)...

Figure 23.25. Glutamate Formation. Conversion of proline and arginine into glutamate.

Vitamin K-deficiency arising from antibiotic therapy decreases y-carboxy-glutamate formation... 

The equilibrium for the reaction is greatly in favor of glutamate formation. From the equation above... 

GDH s of higher plants may bear some relationship to those isolated from Chlorella pyrenoidosa (51). A constitutive enz3rme, active with both NADH and NADPH, is separable by ion-exchange chromatography from an NADPH-specific enzyme that is induced by ammonia. However, glutamate synthase of higher plants may be the primary catalyst involved in glutamate formation (6 ). 

Glutamate formation - Glutamate dehydrogenase catalyzes the reductive amination of... 

Two observations indicate that aspartate is formed primarily by a transamination reaction, probably from glutamate, rather than by a direct amination with NH4 in A. cylindrica. First, N-label in aspartate was reduced more than 90% by the presence of aminooxy acetate, while labeling of glutamate and glutamine was not reduced (IS). Second, [ N]aspartate was not detected when glutamate formation was inhibited either directly, by azaserine, or indirectly, when glutamine s)mthesis was inhibited by methionine sulfoximine (13). Moreover, activity of a glutamate-aspartate aminotransferase reaction has been detected in vitro in two strains of A. cylindrica (1,26). 

EnTymes of Glutamate Formation Glutamate Dehydrogenase, Glutamine... 

The two amide-transferring enzymes purporting to use asparagine or a substrate, were both assayed by measuring NADH oxidation rather than by glutamate formation (Lea and Miflin, 1974). 

I. (1965) Comparative studies on the mechanism of microbial glutamate formation. I. Pathway of glutamate formation from glucose in Brevibacterium flavum and in Micrococcus glutami-cus. J. Gen. Appl. Microbiol, 11 (4), 285-294. 

Shiio I, Otsuka SI, Takahashi M. (1962). Effect of biotin on the bacterial formation of glutamic acid. I. Glutamate formation and cellular premeabUity of amino acids. J Biochem, 51, 56-62. 

Conn, ed.), pp. 249-268. Academic Press, New York 1981 Stenflo, J. Vitamin K, prothrombin and y-carboxyglutamic acid. Adv. Enzymol. 46, 1-31 (1978) Stewart, G. R., Mann, A. F., Fentem, P. A. Enzymes of glutamate formation glutamate dehydrogenase, glutamine synthetase, and glutamate synthase. In The Biochemistry of Plants, Vol. 5, Amino Acids and Derivatives (J. B. Miflin, ed.), pp. 271-327. Academic Press, New York 1980... 

Although the equilibrium of this reaction is very much in favour of glutamate formation, in the cell the rapid removal of the 2-oxoglutarate and NAD(P)H allows the enzyme to function efficiently in the direction of glutamate deamination. Liver glutamate dehydrogenase is a very active enzyme, and the reaction is not rate-limiting for amino acid deamination. 

More recently, Rowsell (306) has found that glutamate formation by transamination with rat liver and kidney preparations occurs at a faster rate for all L-a-amino acids tested than the rate of aerobic oxidation of these amino acids. In addition, the rates of transamination of L-a-amino acids with a-ketoglutarate were found to be comparable to the rates of ammonia or urea formation in oxidative deamination in slices. The further observations by Rowsell (307) that many L-a-amino acids can transami-nate with pyruvate in rat liver preparations has led to the suggestion that oxidative deamination of some L-a-amino acids may involve initial transamination with pyruvate. It was found that transamination of some L-a-amino acids with pyruvate occurred more rapidly than the aerobic oxidation of the L-amino acids. The resulting alanine formed would then he transaminated with a-ketoglutarate by glutamic-pyruvic transaminase. 

---