title: Sucrose-phosphate synthase is dephosphorylated by protein phosphatase 2A in spinach leaves. Evidence from the effects of okadaic acid and microcystin.
abstract: Sucrose-phosphate synthase (SPS) purified from spinach leaves harvested in the dark, was activated by mammalian protein phosphatase 2A (PP2A). Activation of SPS in a fraction from darkened spinach leaves was largely prevented by either okadaic acid or microcystin-LR (specific inhibitors of PPI and PP2A), while inhibitor-2 (a PP1 inhibitor) or Mg2+ (essential for PP2C) were ineffective. In vivo, okadaic acid and microcystin-LR prevented the light-induced activation of SPS and decreased sucrose biosynthesis and CO2 fixation. It is concluded that PP2A is the major SPS phosphatase in spinach. This study is the first to employ microcystin-LR for modulating protein phosphorylation in vivo.
authors.affiliation: Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, FRG.
authors.forename: G
authors.initials: G
authors.lastname: Siegl
authors.forename: C
authors.initials: C
authors.lastname: MacKintosh
authors.forename: M
authors.initials: M
authors.lastname: Stitt
mesh_terms: D000818:Animals; D000458:Cyanobacteria; D004789:Enzyme Activation; D004988:Ethers, Cyclic / Q000494:pharmacology; D005964:Glucosyltransferases / Q000302:isolation & purification / Q000378:metabolism*; D008387:Marine Toxins / Q000494:pharmacology; D052998:Microcystins; D019319:Okadaic Acid; D010456:Peptides, Cyclic / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D010788:Photosynthesis / Q000502:physiology; D010944:Plants / Q000201:enzymology*; D054648:Protein Phosphatase 2
chemical_list: D004988:Ethers, Cyclic; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D019319:Okadaic Acid; D005964:Glucosyltransferases; C022698:sucrose-phosphate synthase; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; C057862:cyanoginosin LR