Preparation and Properties of M-Line Proteins

This chapter provides the preparation and properties of M-Line proteins. Neither the protein composition nor the detailed function of the M line, the electron-dense structure running transversely through the middle of the H-zone of the sarcomere of cross-striated muscle, is yet fully known. So far only two proteins—the M-type isoprotein of creatine kinase (MM-CK) and the M_r = 165,000 protein now called myomesin—have been identified as true M-line proteins. The procedures for the preparation of total creatine kinase from rabbit muscle, from chicken skeletal and heart muscle as well as from chicken brain is described in this chapter.The purification of the M-line MM-CK is best achieved by first preparing well-washed isolated myofibrils from which MM-CK can then be extracted. It is found that ability of antibodies to distinguish between the MM and the BB isoenzymes of CK can be used to detect specifically one or the other homodimeric enzyme by several immunological techniques, such as immune overlay technique, indirect immunofluorescence technique, and immune electron microscopy.