Protein tyrosine phosphorylation in normal rat tissues.

1. Exogenous and endogenous tyrosine protein phosphorylation activities were examined in soluble and particulate fractions from various normal tissues by using poly-[Glu-80Na, Tyr20] and a monoclonal antibody specific for phosphotyrosine. 2. Phosphorylation of the exogenous substrate by the particulate forms of TPKs was 2- to 10-fold higher than by soluble forms. The activities of particulate and soluble enzymes decreased in the following order: spleen > (thymus = kidney) > testes > or = (pancreas = liver = brain) > heart. 3. The level of endogenous phosphorylation in the tissues decreased respectively in the following order: thymus > brain > or = (pancreas = liver) > spleen > testes > kidney > heart for the particulate fractions, and spleen > thymus > brain > pancreas > or = liver > testes > kidney > heart for the soluble fractions. 4. A large number of phosphotyrosine-containing proteins were detected. In addition, several phosphotyrosine-containing proteins of similar molecular weight were found in different tissues and fractions.