MOBILITY OF CREATINE-PHOSPHOKINASE AND BETA-ENOLASE IN CULTURED MUSCLE-CELLS

The diffusion of p-enolase and creatine phosphokinase in muscle cells has been studied by modulated fringe pattern photobleaching. p-Enolase is mobile in the sarcoplasm. At 20 degrees C, the diffusion coefficie nt is 13.5 +/- 2.5 mu m(2) s(-1) in the cytosol and 56 mu m(2) s(-1) i n aqueous media. As in the case of dextrans of the same hydrodynamic r adius, its mobility is hindered by both the crowding of the fluid phas e of the cytoplasm and the screening effect due to myofilaments. A fra ction of creatine phosphokinase is mobile in the sarcoplasm. Its diffu sion coefficient in the cytosol, 4.5 +/- 1 mu m(2) s(-1), is lower tha n that of the dextran of equivalent size. The other fraction (20 to 50 %) is very slightly mobile, with an apparent diffusion coefficient var ying from 0.0035 to 0.043 mu m(2) s(-1). This low mobility might be at tributed to exchange between free and bound creatine phosphokinase. Th e bound fraction of the endogenous enzyme was localized by immunocytof luorescence on the cultured muscle cells. Our results favor a localiza tion of bound cytosolic creatine phosphokinase on the M-line and a dif fuse distribution in all myotubes.