Glutamine formation

Figure 8.17 The metabolism of branched-chain amino acids in muscle and the fate of the nitrogen and oxoacids. The a-NH2 group is transferred to form glutamate which is then aminated to form glutamine. The ammonia required for aminab on arises from glutamate via glutamate dehydrogenase, but originally from the transamination of the branded chain amino acids. Hence, they provide both nitrogen atoms for glutamine formation.

Glutamine synthetase activity was determined by following glutamine formation. The reaction contained 50 mM Hepes-NaOH (50 mM). The reaction was started by addition of ATP and stopped after 15 minutes of incubation at 30°C by addition of 0.6 mL of 1 N HC1. 

The add-base metabolism is influenced by the pH- and HCOs -regulated switchover of ammonium detoxification from urea to glutamine formation. In acidosis, bicarbonate is conserved by curbing hepatic urea synthesis in alkalosis, however, bicarbonate is consumed by enhancing hepatic urea synthesis, (l, 34, 35)... 

The place of L-glutamine in hyaluronate synthesis is shown by experiments with methionine sulfoxide. Since methionine sulfoxide (2-amino-4-methylsulfinylbutyric acid) inhibits L-glutamine formation the addition of the sulfoxide to a culture of hemolytic streptococci inhibits hexosamine synthesis and, consequently, hyaluronate formation. This inhibition can take place at concentrations of methionine sulfoxide which are low enough not to inhibit hyaluronate synthesis with L-glutamine. ... 

Adenosine-5-triphosphoric acid, magnesium sulfate, and cysteine bring about L-glutamine formation from ammonium L-glutamate. However, significant hexosamine synthesis is not observed when these three substances are incubated with ammonium L-glutamate in the presence of a residue-free supernatant from crushed, bacterial cells. L-Glutamine stimu-... 

Glutamine formation - Glutamine synthetase catalyzes the following reaction ... 

The major route of valine and isoleucine catabolism in skeletal muscle is to enter the TCA cycle as succinyl CoA and exit as a-ketoglutarate to provide the carbon skeleton for glutamine formation (see Fig. 42.9). Some of the glutamine and CO2 that is formed from net protein degradation in skeletal muscle may also arise from... 

Fig. 42.10. Formation of glutamine from the amino groups of BCAA. The BCAA are first transaminated with a-ketoglutarate to form glutamate and the branched chain a-keto acids. The glutamate nitrogen can then follow either of two paths leading to glutamine formation. TA = transamination OAA = oxaloacetate a-KG = a-ketoglutarate.

Biolo G, Fleming RY, Maggi SP, et al. Inhibition of muscle glutamine formation in hyper-... 

Glutamine formation Glutamate disappearance (micro- disappearance (micromoles) moles) (micromoles)... 

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