MYOSIN LIGHT CHAIN PHOSPHORYLATION AND PHOSPHORYLASE-A ACTIVITY IN RAT EXTENSOR DIGITORUM LONGUS MUSCLE

Phosphorylation of the 18,500 dalton light chain of myosin and conversion of phosphorylase b to a were examined in relation to isometric tension development. Following a l sec tetanic contraction, light chain phosphate content increased from a pre-tetanic value of 0.10 to 0.75 mol phosphate/mol at 7 sec; phosphorylase a activity (ratio of activity -5′AMP +5′AMP) increased from 0.03 to 0.42 at 4 sec and decreased to control values within 20 sec. Light chain phosphate content, however, declined much more slowly and correlated to post-tetanic potentiation of peak twitch tension. Our results suggest light chain phosphorylation is not obligatory for contraction but may play a role in post-tetanic potentiation. © 1979.