Identification of myosin in Nitella flexilis.

A myosin B-like protein was extracted from the alga Nitella flexilis. SDS-polyacrylamide gel electrophoresis revealed the presence of myosin heavy chain and actin as the main components. At high ionic strength, its ATPase [EC 3.6.1.3] reaction was activated by EDTA or Ca2+ and inhibited by Mg2+. At low ionic strength, superprecipitation was induced by the addition of ATP. Myosin was purified from Nitella myosin B. The molecular weight of the heavy chain of Nitella myosin, estimated by SDS-gel electrophoresis, was slightly higher than that of skeletal muscle myosin. At low ionic strength, Nitella myosin aggregated to form bipolar filaments about 0.2 micron long. At high ionic strength, its ATPase reaction was activated by EDTA or Ca2+, and inhibited by Mg2+. The Mg2+-ATPase reaction of Nitella myosin was activated by skeletal muscle F-actin.