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item Huber, Steven

Submitted to: Molecular and Cellular Proteomics
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2003
Publication Date: 10/1/2003
Citation: Huber, S.C. 2003. Phosphorylation of metabolic enzymes: effects on activity, localization and degradation [abstract]. Molecular and Cellular Proteomics. 2:679.

Interpretive Summary:

Technical Abstract: Protein phosphorylation can affect enzymatic activity, protein localization and protein:protein interactions. With sucrose synthase (Sus), phosphorylation of a major site (Ser-15) affects the conformation of the N-terminus and may influence the association of this soluble, globular protein with cellular membranes. Recent results suggest that phosphorylation of specified sites on certain enzymes may target the proteins for degradation via the ubiquitin/26S proteasome system. This appears to be the case for Sus, nitrate reductase (NR) and cytosolic pyruvate kinase. In the case of Sus, phosphorylation of Ser-170 appears to be the 'trigger,' and phosphorylation of this site in vivo may normally be restricted by endogenous binding proteins. In the case of NR, phosphorylation of Ser-543 is involved in regulation of activity and perhaps also degradation. When a leaf is darkened, phosphorylation of Ser-543 occurs and completes the binding site for a 14-3-3 protein, which binds to form an inactive complex (this is the basis for dark inactivation of the enzyme). However, recent results suggest that phospho-NR, when not complexed with a 14-3-3 protein, may be rapidly degraded. This could provide a general mechanism to insure a balance is maintained between 14-3-3s and their target proteins. Thus, as in animals, phosphorylation of plant enzymes can have multiple effects and some phosphorylation sites (but not all) may represent "phospho-degrons."