A newly synthesized selective casein kinase I inhibitor, N-(2-aminoethyl)-5-chloroisoquinoline-8-sulfonamide, and affinity purification of casein kinase I from bovine testis

When screening various isoquinolinesulfonamide compounds which we synthesized, CKI-7, N-(2-amino-ethyl)-5-chloroisoquinoline-8-sulfonamide, was found to have a potent inhibitory action against Casein Kinase I and a much weaker effect on Casein Kinase II and other protein kinases. Kinetic analysis indicated that CKI-7 inhibited Casein Kinase I competitively with respect to ATP and that the Ki values were 8.5 microM for Casein Kinase I and 70 microM for Casein Kinase II. An affinity chromatography absorbent was synthesized by coupling CKI-8 (1-(5-chloroisoquinoline-8-sulfonyl], a derivative of CKI-7, to cyanogen bromide-activated Sepharose 4B. Partially purified Casein Kinase I from bovine testis was subjected to affinity chromatography. Analysis of the purified Casein Kinase I by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate revealed a single band with molecular weight 37,000. These newly synthesized compounds, CKI-7 and CKI-8, should serve as useful tools for elucidating the biological significance of Casein Kinase I-mediated reactions.