Phosphorylation of paramyosin and its possible role in the catch mechanism

Paramyosin isolated from the adductor muscle of Mercenaria mercenaria was shown to contain three to five phosphate groups/molecule; the actual number varied depending on the method used to extract the protein. Dephosphorylation resulted in an increase in the solubility of paramyosin near pH 7 and near physiological ionic strength. This behavior suggests that the number of phosphates/molecule may be a determining factor in the aggregation behavior of paramyosin-containing myofilaments. Thus, phosphorylation may be involved in catch contractions since correlations have been demonstrated earlier between catch contraction of molluscan muscles and aggregation properties of paramyosin (Ruegg, J. C. (1971) Physiol. Rev. 51, 201-249).