TBB is an ATP/GTP-competitive inhibitor of casein kinase 2 (CK2; IC50 = 900 μM for rat liver CK2). It less potently inhibits CCK2/cyclin A, GSK3β, and phosphorylase kinase (IC50 = 15.6, 11.2, and 8.7 mM, respectively). It is much less effective against a range of other kinases.
