Glutamine synthetase quaternary

The kinetic reaction mechanism appears to be random, and for the reaction to proceed, all substrates must reside as a E-D-Ala-D-Ala-MgATP quaternary complex. Except for its activation of an a-carboxylate to form a peptide bond, the enzyme s mechanism appears to be completely analogous to that catalyzed by glutamine synthetase, which forms a y-glutamyl-phosphate intermediate. There is strong evidence for the participation... 

There are two cation-binding sites per subunit, classified nL and n2. The n, site is a structural site, which may involve the reorientation of a glutamate carboxyl group. Metals bind first at this site. The n2 site is the catalytic site and may bind metal or metal-nucleotide. Co111 and Cr111 can be incorporated into the nj metal-binding sites in un-adenylylated glutamine synthetase from E. co/i.318 Both derivatives were inactive, but were able to bind Mn2+ at the n2 site. Comparison of the quaternary enzyme-Crin-Mnn-ADP (which shows spin-spin interaction between the two metal centres) with enzyme-Com-Mnn-ADP leads to an estimate of the distance between n, and n2 sites of 7 2 A. 

Figure II-4 Examples of the quaternary structure of proteins, (a) A drawing of glutamine synthetase of coli showing the orientation of the 12 identical subunits of the enzyme. (b) A drawing of aspartate transcarbamylase of coli showing the proposed orientation of the 6 catalytic subunits (labeled C, each MW = 33,000), and 6 regulatory subunits (labeled R, each MW =...

---

See also in sourсe #XX -- [ ]

---