Biochemistry, Department of


Document Type


Date of this Version



Plant Physiol. (1989) 89, 238-243


Copyright American Society of Plant Biologists. Used by permission.


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.