A GTP-specific protein kinase in plasma membranes of mouse fibroblasts

Abstract

Endogenous protein phosphorylation in plasma membranes isolated from SV 40-transformed mouse fibroblasts was studied in the presence of [γ- 32P]GTP. The phosphoprotein pattern showed one main component with 100 k which could not be phosphorylated with ATP. Optimal phosphorylation of pp 100 was dependent on protein concentration. Strict substrate specificity of the corresponding endogenous kinase could be demonstrated by comparative electrophoresis with a plasma membrane sample phosphorylated with [γ- 32P]ATP and by isotope dilution experiments. GTP-specific phosphorylation of pp 100 was not dependent on cyclic nucleotides but influenced by GDP, GMP and AMP.