Association of chicken pectoralis muscle phosphorylase with the Z-line and the M-line of myofibrils: comparison with 'amorphin', the amorphous component of the Z-line.

By immunofluorescence technique, glycogen phosphorylase, one of the soluble glycolytic enzymes, was shown to be localized in the Z-line of chicken pectoralis muscle myofibrils, in addition to the M-line, as previously reported by Heizmann, C.W. and Eppenberger, H.M. (Heizmann, C.W. and Eppenberger, H.M. (1978) J. Biol. Chem. 253, 270-277). After extraction of thick filaments by a solution containing pyrophosphate and high salt (Hasselbach-Schneider solution), or after extraction of thin and thick filaments by a solution containing 0.6 M KI, phosphorylase still remained in the Z-line. Amorphin (Mr 85 000) was reported by Chowrashi, P.K. and Pepe, F.A. (Chowrashi, P.K. and Pepe, F.A. (1982) J. Cell Biol. 94, 565-573) as a new Z-line amorphous component. The amino acid composition of amorphin reported by them was very similar to that of phosphorylase b reported by Heizmann and Eppenberger. The partially purified 85 kDa protein, according to Chowrashi and Pepe, showed cross-reactivity to anti-phosphorylase serum and phosphorylase activity. Although amorphin was reported to be eluted from DEAE-column chromatography around the gradient of 0.5 M KCl, little protein was eluted around 0.5 M KCl in our experiments, and the 85 kDa protein which we identified as phosphorylase b was eluted around 0.2 M KCl. Hence, it should be said that the major 85 kDa protein extracted according to Chowrashi and Pepe was phosphorylase b.