There are several regulatory proteins other than well-known troponin and tropomyosin in muscle. These are small in contents, but play a role mainly in regulating ordered structure of muscle. The proteins locating in the A band of myofibril are M-protein, C-protein, γ-component and J-protein. Those in I band are actinins, β, γ-, and 10S. α-Actinin is a Z-line substance. In this review the nature and function of these minor regulatory proteins are critically reviewed.
