Is smooth muscle appear to lack tropin?

Smooth muscle does not contain troponin, which is a regulatory protein found in skeletal and cardiac muscle. Instead, smooth muscle contraction is regulated by the protein calmodulin, which interacts with calcium ions to activate myosin light chain kinase. This mechanism allows smooth muscle to contract in response to various stimuli, such as hormones and neurotransmitters, without the troponin-tropomyosin complex found in striated muscles.