COMPARISON OF THE SUBSTRATE SPECIFICITIES OF CAMP-DEPENDENT PROTEIN-KINASE FROM BOVINE HEART AND ASCARIS-SUUM MUSCLE

The catalytic subunits of cAMP-dependent protein kinases (protein kina se A) from bovine heart and Ascaris suum muscle exhibit only 48% seque nce identity and show quantitative differences in substrate specificit y, These differences were not obvious at the level of short synthetic substrate peptides but were distinct for some protein substrates. Phos phofructokinase from Ascaris, a physiological substrate, was a better substrate for the protein kinase from the nematode in comparison to th e mammalian protein kinase due to a 10-fold lower Michaelis constant. Selective phosphorylation by the two kinases was also observed with so me in vitro substrates. In addition, quantitative differences in the i nteractions between R- and C-subunits from Ascaris and bovine heart we re observed, However, several synthetic peptides whose sequence reflec ted the phosphorylation site of Ascaris suum phosphofructokinase (AKGR SDSIV), or variations of it, were phosphorylated with the same effici ency by both protein kinases. Based on the data the following are conc luded: (1) In agreement with the conservation of structure in the cata lytic cleft, the recognition of substrates by protein kinases from phy logenetically distant organisms exhibits similarity, (2) Non-conserved parts of the surface of the protein kinase molecule may contribute to binding of protein substrates and thus to selective recognition.