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PLANT PHYSIOLOGY , Vol 111, Issue 4 1169-1175, Copyright © 1996 by American Society of Plant Biologists

BIOCHEMISTRY AND ENZYMOLOGY

Isolation and Characterization of Glutamine Synthetase from the Marine Diatom Skeletonema costatum

D. L. Robertson and R. S. Alberte
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637 (D.L.R.)

Two peaks of glutamine synthetase (GS) activity were resolved by anion-exchange chromatography from the marine diatom Skeletonema costatum Grev. The second peak of activity accounted for greater than 93% of total enzyme activity, and this isoform was purified over 200-fold. Results from denaturing gel electrophoresis and gel-filtration chromatography suggest that six 70-kD subunits constitute the 400-kD native enzyme. The structure of the diatom GS, therefore, appears more similar to that of a type found in bacteria than to the type common among other eukaryotes. Apparent Michaelis constant values were 0.7 mM for NH4+, 5.7 mM for glutamic acid, and 0.5 mM for ATP. Enzyme activity was inhibited by serine, alanine, glycine, phosphinothricin, and methionine sulfoximine. Polyclonal antiserum raised against the purified enzyme localized a single polypeptide on western blots of S. costatum cell lysates and recognized the denatured, native enzyme. Western analysis of the two peak fractions derived from anion-exchange chromatography demonstrated that the 70-kD protein was present only in the later-eluting peak of enzyme activity. This form of GS does not appear to be unique to S. costatum, since the antiserum recognized a similar-sized protein in cell lysates of other chromophytic algae.


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 Mol Biol EvolHome page
D. L. Robertson and A. Tartar
Evolution of Glutamine Synthetase in Heterokonts: Evidence for Endosymbiotic Gene Transfer and the Early Evolution of Photosynthesis
Mol. Biol. Evol., May 1, 2006; 23(5): 1048 - 1055.
[Abstract] [Full Text] [PDF]

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 Plant Physiol.Home page
Y. Gao, O. M.E. Schofield, and T. Leustek
Characterization of Sulfate Assimilation in Marine Algae Focusing on the Enzyme 5'-Adenylylsulfate Reductase
Plant Physiology, July 1, 2000; 123(3): 1087 - 1096.
[Abstract] [Full Text]


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