Myosin in Cultured Fibroblasts

Myosin has been identified in three independently derived cell lines of fibroblasts: normal rat kidney cells, mouse 3T3 cells, and mouse L cells. A quantitative two-step procedure for its extraction from as little as 200 mg of cultured fibroblasts (wet weight) has been developed. Myosin constitutes from 0.5 % to over 3 % of the total fibroblast protein. Cell fractionation suggests that the myosin principally resides in the cytoplasm. One virus-transformed, normal rat kidney cell line contained one-half of the myosin of its NRK parent. Treatment of L cells during culture with N6,O2'-dibutyryl cyclic adenosine 3',5'-monophosphate and theophylline had no effect on their myosin content. Actin and tubulin were identified in L cells.