Protein kinase inhibitors, widely exploited for elucidation of the biological functions of kinases, have more recently come under active consideration as potential chemotherapeutic agents for tumour and other diseases. A brief overview is presented of diverse approaches to the design and development of selective protein kinase inhibitors, and related problems such as donor and acceptor specificities, stereochemical aspects, emerging relationships between protein, sugar and nucleoside kinases. In particular, and contrary to popular belief that ATP-competitive inhibifcrs cannot be selective because of the close homology of the ATP catalytic sites, numerous examples are presented of such inhibitors which are both potent and selective for a given kinase or class of kinases. Some of these are undergoing preclinical trials. Attention is also directed to the role of cellular and viral protein kinases in the ljfe cycle of viruses, and the potential of these enzymes, especially those encoded by, and essential for replication of, a given virus as targets for antiviral chemotherapy.
Two yeast casein kinase type-I sp«cies of 45 kDa and 27 kDa (CK1) were purified to apparent homogeneity and used for investigation of their immunological affinity. Antiscra against the two kinases were isolated; the antibody agaiast the 45 kDa kinase did not react with the 27 kDa enzyme. The 27 kDa casein kinase was recognized only by its own antibody. The obtained data strongly suggest that the low molecular mass CK-1 is not a proteolytic product of the 45 kDa kinase species.