Classes
There seem to be three different classes of GS:
- Class I enzymes (GSI) are specific to prokaryotes, and are oligomers of 12 identical subunits. The activity of GSI-type enzyme is controlled by the adenylation of a tyrosine residue. The adenylated enzyme is inactive.
- Class II enzymes (GSII) are found in eukaryotes and in bacteria belonging to the Rhizobiaceae, Frankiaceae, and Streptomycetaceae families (these bacteria have also a class-I GS). GSII are decamer of identical subunits.
Plants have two or more isozymes of GSII, one of the isozymes is translocated into the chloroplast.
- Class III enzymes (GSIII) has, currently, only been found in Bacteroides fragilis and in Butyrivibrio fibrisolvens. It is a double-ringed dodecamer of identical chains. It is much larger (about 700 amino acids) than the GSI (450 to 470 amino acids) or GSII (350 to 420 amino acids) enzymes.
While the three classes of GS's are clearly structurally related, the sequence similarities are not so extensive.
Read more about this topic: Glutamine Synthetase
Famous quotes containing the word classes:
“There are two classes of men called poets. The one cultivates life, the other art,... one satisfies hunger, the other gratifies the palate.”
—Henry David Thoreau (1817–1862)
“Is a man too strong and fierce for society, and by temper and position a bad citizen,—a morose ruffian, with a dash of the pirate in him;Mnature sends him a troop of pretty sons and daughters, who are getting along in the dame’s classes at the village school, and love and fear for them smooths his grim scowl to courtesy. Thus she contrives to intenerate the granite and the feldspar, takes the boar out and puts the lamb in, and keeps her balance true.”
—Ralph Waldo Emerson (1803–1882)
“There were three classes of inhabitants who either frequent or inhabit the country which we had now entered: first, the loggers, who, for a part of the year, the winter and spring, are far the most numerous, but in the summer, except for a few explorers for timber, completely desert it; second, the few settlers I have named, the only permanent inhabitants, who live on the verge of it, and help raise supplies for the former; third, the hunters, mostly Indians, who range over it in their season.”
—Henry David Thoreau (1817–1862)