Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 277, Issue 9, Pages 7231-7238Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M110926200
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Funding
- NIDDK NIH HHS [DK 54423] Funding Source: Medline
- NATIONAL INSTITUTE OF DIABETES AND DIGESTIVE AND KIDNEY DISEASES [R01DK054423] Funding Source: NIH RePORTER
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Carbamoyl phosphate synthetases (CPSs) utilize either glutamine or ammonia for the ATP-dependent generation of carbamoyl phosphate. In glutamine-utilizing CPSs (e.g. the single Escherichia coli CPS and mammalian CPS II), the hydrolysis of glutamine to yield ammonia is catalyzed at a triad-type glutamine amidotransferase domain. Non-glutamine-utilizing CPSs (e.g. rat and human CPS I), lacking the catalytic cysteine residue, can generate carbamoyl phosphate only in the presence of free ammonia. Frog CPS I (fCPS I), unlike mam- malian CPS Is, retains most of the glutamine amidotransferase residues conserved in glutamine-utilizing CPSs, including an intact catalytic triad, and could therefore be expected to use glutamine. Our work with native fCPS I provides the first demonstration of the inability of this enzyme to bind/utilize glutamine. To determine why fCPS I is unable to utilize glutamine, we compared sequences of glutamine-using and non-glutamine-using CPSs to identify residues that are present or conservatively substituted in all glutamine-utilizing CPSs but absent in fCPS I. We constructed the site-directed mutants Q273E, L270K, Q273E/N240S, and Q273E/L270K in E. coli CPS and have determined that simultaneous occurrence of the two substitutions, GIn --> Glu and Leu --> Lys, found in the frog CPS I glutamine amidotransferase domain are sufficient to eliminate glutamine utilization by the E. coli enzyme.
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