Troponin is the central regulatory protein of striated muscle contraction. Tn consists of three components: Tn-I which is the inhibitor of actomyosin ATPase, Tn-T which contains the binding site for tropomyosin and Tn-C. The binding of calcium to Tn-C abolishes the inhibitory action of Tn on actin filaments. Causes an allergic reaction in human. Binds to IgE in 11% of the 46 patients tested allergic to storage mite T.putrescentiae. IgE reactivity is calcium-dependent. Addition of 10 mM CaCl(2) increases the intensity of IgE-binding approximately 2-fold in 4 sera out of 5 tested. Belongs to the troponin C family.