What is the difference between a "voluntary" and an "involuntary" muscle?

Voluntary actions are actions that are made consciously that the body knows it is about to do. An example is walking - the muscles in your leg move voluntarily.

Involuntary actions are actions that are made subconsciously and can not be controlled or stopped. An example is your heart beating, your breathing, etc

hope this helps. 

Pro insulin undergoes extensive posttranslational modification along the production pathway .