A new 220,000 dalton protein located in the Z lines of vertebrate skeletal muscle.

A new protein with a chain weight of approximately 220,000 was isolated from 0.6 M KI extracts of I-Z-I brushes of rabbit and chicken skeletal muscles, using (NH4)2SO4 precipitation and three column chromatographic procedures in succession. It was only possible to separate the high molecular weight protein from actin and alpha-actinin in the presence of 6 M urea or 0.1% sodium dodecyl sulfate (SDS). The purified protein migrated as a single band on SDS gel electrophoresis. The amino acid composition of the 220,000 dalton protein was distinct from any known proteins found in myofibrils, e.g., alpha-actinin and actin binding protein (ABP; filamin). An indirect immunofluorescence technique revealed that the new protein was exclusively located in the Z lines of myofibrils of chicken breast muscle. There is, however, a possibility that the 220,000 dalton protein is identical with synemin recently isolated from chicken gizzard (Granger, B.L. and Lazarides, E. (1980) Cell 22, 727).