Stimulation in vitro of Rabbit Erythrocyte Cytosol Phospholipid-dependent Protein Kinase Activity

L-Thyroxine (T4) and 3,3',5-L-triiodothyronine (T3) at 10(-10) M stimulated phospholipid- and Ca2+-dependent protein kinase activity in rabbit red cell cytosol in vitro by 151 and 176%, respectively. Kinase of 30-fold greater specific activity, developed with 0.4 mM NaCl from cytosol applied to DEAE-cellulose, was also stimulated up to 2-fold by thyroid hormone. Hormone enhancement of kinase activity occurred after 60 min of incubation at 37 degrees C prior to enzyme assay. Thyroid hormone analogues triiodothyroacetic acid, 3,5-dimethyl-3'-isopropyl-L-thyronine, D-T3, D-T4, and 3,3',5'-L-triiodothyronine (reverse T3) were inactive. These results support a role for thyroid hormone endogenously in regulation of phospholipid-dependent protein kinase activity.