Abstract:
:Rat liver glutamine synthetase (s(20,w) 15.0 S; MW about 352,000) resembles ovine brain glutamine synthetase in that it (a) has 8 subunits, (b) acts on both L- and D-glutamate and certain glutamate analogs (e.g., beta-glutamate, cis-cycloglutamate, and alpha-methyl-L-glutamate), and (c) is irreversibly inhibited by L-methionine-S-sulfoximine. The liver enzyme (but not the brain enzyme) is (a) markedly activated by alpha-ketoglutarate and less so by citrate, and (b) inhibited noncumulatively by glycine and alanine, in the presence of Mn(++) but not Mg(++); inhibition increases with increasing concentrations of glutamate. These regulatory phenomena seem to be correlated with metabolically related enzymes, e.g., glutamine transaminase. Both liver and brain glutamine synthetases are inhibited by carbamyl phosphate (with Mn(++) but not with Mg(++)), which provides a means for controlling glutamine for pyrimidine biosynthesis. Addition of Mn(++) to the Mg(++)-synthetase system, even at Mg(++): Mn(++) ratios of 1000, markedly inhibits synthesis by both brain and liver enzymes. This finding, and the fact that Mn(++) promotes sensitivity to the negative effectors, indicates that Mn(++) plays a central role in the regulation of glutamine synthetase. Properties of the glutamine synthetases that have been isolated from mammalian, plant, and bacterial cells are compared. They are similar with respect to subunit size, substrate specificity, inhibition by methionine sulfoximine, and Mn(++)-sensitive inhibition by glycine, alanine, and carbamyl phosphate, but differ in certain other regulatory phenomena and in subunit structure.
journal_name
Proc Natl Acad Sci U S Aauthors
Tate SS,Meister Adoi
10.1073/pnas.68.4.781subject
Has Abstractpub_date
1971-04-01 00:00:00pages
781-5issue
4eissn
0027-8424issn
1091-6490journal_volume
68pub_type
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