Phosphorylation of membrane proteins in response to heat shock in cultured pear cells

Abstract

Phosphorylation of membrane proteins was studied in suspension cultured pear ( Pyrus communis L. cv. Passe Crassane) cells in response to a heat shock of 38°C for 2 h. Protein kinase activity was assayed in the membrane preparation, and was significantly reduced by heat treatment of the cells. The presence of EGTA in the assay medium reduced kinase activity about 60% in membranes from unheated cells and 40% in membranes of heated cells. In vitro labelling of membrane preparations with [ 32P]ATP for 60 s resulted in some bands more heavily labelled in heated membranes than in unheated ones. When in vivo labelling of proteins with 32P was done during the second hour of heating, there were differences in labelled membrane proteins, compared with membrane proteins from unheated cells. Incorporation of [ 35S]methionine during the second hour of treatment resulted in the synthesis of a number of heat shock proteins, two of which had the same M r as phosphorylated proteins. These results indicate that membrane protein phosphorylation may be involved in the response of cells to heat shock.