Glutamate from glutamine

Glutamate from glutamine Glutamine can be a precursor for the synthesis of glutamate, with the reaction of glutamate synthase, also known as GOGAT (glutamine  

The preceding reactions indicate that two ways exist of making glutamate  

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Mitochondria of hair cells were strongly immunolabelled for glutamate (Fig. IB). This is consistent with the idea that these organelles are responsible for the synthesis of transmitter glutamate from glutamine (Chapter 1 also see below). 

NH4" absorbed by mycelia, or derived from NO, reduction, is rapidly assimilated into glutamate and glutamine, which are then used to synthesize other... 

The excitatory neurotransmitter in brain, glutamate, is synthesised from glutamine in a reaction catalysed by the enzyme glntaminase. This enzyme is inhibited by a high concentration of ammonia, which could lead to a chronic depletion of this excitatory neurotransmitter. 

Scheme 1 Formation of Pyroglutamic Acid from Glutamine, Glutamic Acid, and Related Derivatives...

Plasma that cannot be analyzed instantaneously should be kept frozen at -20°C. Glutamine is particularly liable to decomposition, thereby yielding glutamic acid, but also the ninhydrin-negative pyroglutamic acid. It has even been claimed that y-aminobutyric acid can be formed from glutamine. Even at -20°C the decomposition of glutamine cannot be stopped completely. 

In bacteria and plants, glutamate is produced from glutamine in a reaction catalyzed by glutamate synthase. a-Ketoglutarate, an intermediate of the citric acid cycle, undergoes reductive amination with glutamine as nitrogen donor ... 

The amino acid and nucleotide biosynthetic pathways make repeated use of the biological cofactors pyridoxal phosphate, tetrahydrofolate, and A-adenosylmethionine. Pyridoxal phosphate is required for transamination reactions involving glutamate and for other amino acid transformations. One-carbon transfers require S-adenosyhnethionine and tetrahydrofolate. Glutamine amidotransferases catalyze reactions that incorporate nitrogen derived from glutamine. 

All amino acids are derived from intermediates in glycolysis, the citric acid cycle, or the pentose phosphate pathway (Fig. 22-9). Nitrogen enters these pathways by way of glutamate and glutamine. Some pathways are simple, others are not. Ten of the amino acids are just one or several steps removed from the common metabolite from which they are derived. The biosynthetic pathways for others, such as the aromatic amino acids, are more complex. 

FIGURE 22-20 Biosynthesis of histidine in bacteria and plants. Atoms derived from PRPP and ATP are shaded red and blue, respectively. Two of the histidine nitrogens are derived from glutamine and glutamate (green). Note that the derivative of ATP remaining after step (AICAR) is an intermediate in purine biosynthesis (see Fig. 22-33, step ), so ATP is rapidly regenerated. 

Ammonia transport in the blood from the peripheral tissues to the liver occurs by two major mechanisms glutamine can be synthesized from glutamate and ammonia (glutamine synthetase) or pyruvate can be transaminated to alanine. In the liver, the ammonia group is removed from glutamine by glutaminase and from alanine by transamination. 

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