Studies on the mechanism of thyroid hormone stimulation in vitro of human red cell Ca2+-ATPase activity

The stimulation in vitro of human red blood cell Ca2+-ATPase activity by thyroxine (T4) and triiodothyronine (T3) in physiological concentrations is shown to depend upon binding of iodothyronines to red cell membranes. Calmodulin enhances the activity of thyroid hormone in this model system but there is no direct interaction of calmodulin and hormone.