Properties of two high-molecular-mass forms of glyceraldehyde-3-phosphate dehydrogenase from spinach leaf, one of which also possesses latent phosphoribulokinase activity.
Two high-Mr forms of chloroplast glyceraldehyde-3-phosphate dehydrogenase from spinach leaf can be separated by DEAE-cellulose chromatography. One form, the high-Mr glyceraldehyde-3-phosphate dehydrogenase, resembles an enzyme previously described [Yonuschot, G.R., Ortwerth, B.J. & Koeppe, O.J. (1970) J. Biol. Chem. 245, 4193-4198]. The other, a glyceraldehyde-3-phosphate dehydrogenase/phosphoribulokinase complex, is characterised by possession of latent phosphoribulokinase activity, only expressed following incubation with dithiothreitol. This complex is composed not only of subunits A (39.5 kDa) and B (41.5 kDa) characteristic of the high-Mr glyceraldehyde-3-phosphate dehydrogenase, but also of a third subunit, R (40.5 kDa) comigrating with that from the active phosphoribulokinase of spinach. Incubation of the complex with dithiothreitol markedly stimulated both its phosphoribulokinase and NADPH-dependent dehydrogenase activities. This dithiothreitol-induced activation was accompanied by depolymerisation to give two predominantly NADPH-linked tetrameric glyceraldehyde-3-phosphate dehydrogenases (the homotetramer, A4, and the heterotetramer, A2B2) as well as the active dimeric phosphoribulokinase. Incubation of the high-Mr glyceraldehyde-3-phosphate dehydrogenase with dithiothreitol promoted complete depolymerisation yielding only the heterotetramer (A2B2). Possible structures suggested for the glyceraldehyde-3-phosphate dehydrogenase/phosphoribulokinase complex are (A2B2)2A4R2 or (A2B2)(A4)2R2.
Clasper
S
S
Department of Biochemistry, University of Liverpool, England.
Easterby
J S
JS
Powls
R
R
D015153:Blotting, Western; D002848:Chromatography, DEAE-Cellulose / Q000379:methods; D002853:Chromatography, Liquid / Q000379:methods; D004591:Electrophoresis, Polyacrylamide Gel; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000302:isolation & purification* / Q000378:metabolism*; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010770:Phosphotransferases / Q000302:isolation & purification* / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor); D010944:Plants / Q000201:enzymology*
D007527:Isoenzymes; D046911:Macromolecular Substances; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C022390:phosphoribulokinase