Nonenzymatic phosphorylation of tyrosine and serine by ATP is catalyzed by manganese but not magnesium.

Many cellular and retroviral protein-tyrosine kinases display either a requirement or a preference for manganese over magnesium for maximal activity. We have observed that peptides and proteins are non-enzymatically phosphorylated at tyrosine and serine by ATP when heated in the presence of MnCl2 at neutral pH. The extent of the reaction is negligible below 50 degrees C but increases rapidly at higher temperatures. The reaction proceeds in the presence of sodium dodecyl sulfate but is blocked by EDTA. No reaction is observed in the absence of Mn2+, even if Mg2+ is present. Manganese therefore acts as a catalyst for the non-enzymatic reaction, but magnesium does not. We propose that the preference for manganese shown by many protein tyrosine kinases is due at least in part to the intrinsic ability of Mn2+ to catalyze the transfer of phosphate from ATP to a phosphate acceptor such as tyrosine. The nonenzymatic phosphorylation reaction also offers a new synthetic pathway for the preparation of radiolabeled peptides containing phosphotyrosine and phosphoserine.