[Interaction of 8-substituted derivatives and adenosine-3',5'-cyclophosphate esters with protein kinase from pig brain].

A synthesis of previously unknown 8-substituted derivatives and alkyl esters of cyclic adenosine-3',5'-monophosphate, containing reactive groups, was carried out. The interaction of the compounds obtained with a homogeneous preparation of protein kinase from pig brain was studied. It was found that all compounds, with the exception of neutral esters of 3',5'-AMP, activate the enzyme and competitively inhibit 3H-labelled 3',5'-cAMP binding by the regulatory subunit of protein kinase. The activating effect and affinity of 8-(beta-aminoethylamino)-3',5'-cAMP for protein kinase was 10 times lower than that for 3',5'-cAMP and other 8-substituted derivatives of the cyclic nucleotide. It was found that 8-(N-chloroacetylaminoethylamino)-3',5'-cAMP interaction with the enzyme is of irreversible type, which suggest covalent blocking of the nucleophilic group of the 3',5'-cAMP binding site of protein kinase. The data obtained indicate that the 3',5'-cAMP molecule is bound to the regulatory site of protein kinase in the syn-conformation. The previously made assumption on the crucial importance of the negative charge in the 3',5'-cyclophosphate system for the interaction of cyclic AMP with the regulatory subunit of protein kinase has been thus confirmed.