query on C* algebra definition

Question

In the definition of C* algebra there is a Banach algebra together with a map, called involution map, which obey some properties. We denote the map by sending x to x*, called adjoint of x. Now my question is if there is one such involution map in a Banach algebra obeying those properties, then how many such map exist to make the Banach algebra a C* algebra. that is what can we say about the number of involutions if one exist.