I-Protein, a new regulatory protein from vertebrate skeletal muscle. I. Purification and characterization

A new minor regulatory protein designated as I-protein has been isolated from skeletal muscles of the chicken and the rabbit. The yield of purified I-protein was small: 5-10 mg per kg of muscle. I-protein was found to have a molecular weight of 50,000 and high contents of Asp and Glu, accounting for more than one third of the total amino acids.