Which one of the following is absent in smooth muscles?: (A) Actin, (B) Myosin, (C) Troponin, (D) Myosin adenine triphosphatase
Answer is C. (C) Troponin> Smooth muscle have no troponin or tropomyosin, but they have actin and myosin.> They have no sarcoplasmic reticulum, No T-tubule.> No Z lines. The contraction is stimulated by extracellular ca+.> Latching - is the characteristic of smooth muscle. Even after the dephosphorylation of myosin, the cross bridges continue to attach in the same position for some time. There is no fixed tension relationship.