Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

View full-text article in PMC

. 2015 Feb;7(2):a006023. doi: 10.1101/cshperspect.a006023

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

Copyright © 2015 Cold Spring Harbor Laboratory Press; all rights reserved

PMC Copyright notice

Figure 2. — Calcium triggers contraction in striated muscle. (A) Actomyosin in striated muscle. (1) Striated muscle in the relaxed state has tropomyosin covering myosin-binding sites on actin. (2) Calcium binds to troponin C, which induces a conformational change in the troponin complex. This causes tropomyosin to move deeper into the actin groove, revealing the myosin-binding sites. (B) Cross-bridge cycle in striated muscle. (1) Calcium binds to troponin C, causing the conformational shift in tropomyosin that reveals myosin-binding sites on actin. (2) ATP then binds to myosin. (3) ATP is then hydrolyzed. (4) A cross-bridge forms and myosin binds to a new position on actin. (5) Pi is released and myosin changes conformation, resulting in the power stroke that causes the filaments to slide past each other. (6) ADP is then released. (C) Contraction in smooth muscle. In smooth muscle, calcium binds to calmodulin and causes the activation of myosin light chain (MLC) kinase (MLCK). This phosphorylates MLC, which then binds to actin to form phosphorylated actomyosin, enabling the cross-bridge cycle to start.