Chloroplast Thylakoid Protein Phosphatase Is a Membrane Surface-Associated Activity

Authors

Gongqin Sun, University of Nebraska - Lincoln
Doreen Bailey, University of Nebraska - Lincoln
Michael W. Jones, University of Nebraska - Lincoln
John Markwell, University of Nebraska–LincolnFollow

Document Type

Article

Date of this Version

1989

Citation

Plant Physiol. (1989) 89, 238-243

Comments

Copyright American Society of Plant Biologists. Used by permission.

Abstract

Chloroplast thylakoid protein phosphatase activity was measured using ³²P-labeled histone as an exogenous substrate and an assay of the ³²P released involving formation of a phosphomolybdate complex and organic extraction. The activity was liberated from wheat (Triticum aestivum) thylakoids by washing the membranes in NaCI-containing solutions followed by centrifugation. The liberated phosphatase activity had a pH optimum of approximately 6.75, was inhibited by addition of 10 millimolar EDTA or EGTA, and was stimulated by addition of millimolar amounts of dithiothreitol, magnesium, manganese, or calcium ions. The rate of thylakoid protein dephosphorylation was decreased following liberation of a portion of the protein phosphatase activity and was increased by addition of sait-liberated phosphatase fraction. These results suggest that at least a portion of wheat thylakoid protein phosphatase is a peripheral, rather than an integral, membrane protein.