Dephosphorylation of the Thylakoid Membrane Light-Harvesting Complex-II by a Stromal Protein Phosphatase

Authors

Mark E. Hammer, University of Nebraska–Lincoln
Gautam Sarath, University of Nebraska–LincolnFollow
John Markwell, University of Nebraska–LincolnFollow

ORCID IDs

Gautam Sarath

Date of this Version

1995

Comments

Published in Photosynthesis Research 45 (1995), pp. 195-201. Copyright © 1995 Kluwer Academic Publishers. Used by permission.

Abstract

Light-harvesting complex-II (LHC-II) phosphatase activity has generally been examined in the intact thylakoid membrane. A recent report of peptide-phosphatase activity associated with the chloroplast stromal fraction (Hammer, M.E et al. (1995) Photosynth Res 44:107–115) has led to the question of whether this activity is capable of dephosphorylating membrane-bound LHC-II. To this end, heat-treated thylakoid membranes were examined as a potential LHC-II phosphatase substrate. Following incubation of the thylakoid membrane at 60 °C for 15 min, the endogenous protein phosphatase and kinase activities were almost eliminated. Heat-inactivated phosphomembranes exhibited minimal dephosphorylation of the light harvesting complex-II. Peptide-phosphatase activities isolated from the thylakoid and stromal fraction were able to dephosphorylate LHC-II in heat-inactivated phosphomembranes. The stromal phosphatase showed highest activity against LHC-II at pH 9. Dephosphorylation of the LHC-II by the stromal enzyme was not inhibited by molybdate, vanadate or tungstate ions, but was partially inhibited by EDTA and a synthetic phosphopeptide mimicking the LHC-II phosphorylation site. Thus, the previously identified stromal phosphatase does appear capable of dephosphorylating authentic LHC-II in vivo.