Glutamine synthetase reactions

Figure 28-4. The asparagine synthetase reaction. Note similarities to and differences from the glutamine synthetase reaction (Figure 28-2).

The key reaction that links primary and secondary metabolism is provided by the enzyme phenylalanine ammonia lyase (PAL) which catalyzes the deamination of l-phenylalanine to form iran.v-cinnamic acid with the release of NH3 (see Fig. 3.3). Tyrosine is similarly deaminated by tyrosine ammonia lyase (TAL) to produce 4-hydroxycinnamic acid and NH3. The released NH3 is probably fixed by the glutamine synthetase reaction. These deaminations initiate the main phenylpropanoid pathway. 

Experimental demonstration that the Escherichia coli glutamine synthetase reaction operates by a random order of addition of substrates and a random order of release of products. 

Glutamine synthetase reaction intermediate, BOROHYDRIDE REDUCTION Glutamine synthetase UTase/UR enzyme reactions,... 

Depletion of glutamate in the glutamine synthetase reaction may have additional effects on the brain. Glutamate and its derivative y-aminobutyrate (GABA see Fig. 22-29) are important neurotransmitters the sensitivity of the brain to ammonia may reflect a depletion of neurotransmitters as well as changes in cellular osmotic balance. ... 

Fig. 19. Two proposed kinetic schemes for the glutamine synthetase reaction.

The above data, along with other data from Meister s group (102, 103), provided the basis for computer modeling studies (104) of the active site conformations of substrates and intermediates in the glutamine synthetase reaction. The conclusions are that both structures II and III are in the reaction mechanism. 

Wakisaka, S., Y. Ohshima, M. Ogawa, T. Tochikura, andT. Tachiki. 1988. Characteristics and efficiency of glutamine production by coupling of a bacterial glutamine synthetase reaction with the alcoholic fermentation system of baker s yeast. Appl. Environ. Microbiol. 64 2953-2957. 

In another case, y-glutamyl phosphate is believed to be an enzyme-bound intermediate in the glutamine synthetase reaction. 

Meister has more recently studied the glutamine synthetase reaction in considerable detail, and has proposed the following mechanism ... 

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