Alkaline hydrolysis and multiple site autophosphorylation differ for two forms of the epidermal growth factor receptor.

Different tyrosines are autophosphorylated on the native and on the protease-generated 150 kDa forms of the epidermal growth factor receptor. High ATP concentrations increase the apparent molecular weight of already phosphorylated native receptors but not of the 150 kDa form, indicating that only the native receptor has multiple autophosphorylation sites available. The non-identity of the tyrosine-phosphates on the native and 150 kDa receptor forms is seen in their response to alkaline hydrolysis (10% and 40% resistant, respectively). Since the liberated phosphate is peptide bound, the native receptor fails to be alkali-resistant because of which peptide bonds are hydrolyzed.