Epidermal growth factor-stimulated phosphorylation of tyrosine residues on a 120 000 dalton protein in mouse liver plasma membrane subfractions

The addition of Epidermal growth factor (EGF) to mouse liver sinusoidal plasma membrane subfractions, isolated from the blood face of hepatocytes, resulted in a two to threefold increase of 32P incorporation from [γ- 32P ]ATP into a 120 000 dalton protein component. The EGF-stimulation of the phosphorylation of this component was also evidenced in plasma membranes derived from the lateral and biliary faces of hepatocytes. A major phosphoamino acid residue after EGF stimulation was identified as tyrosine. An EGF-enhancement of the phosphorylation of threonine and serine residues also appears to be detectable.