The force-velocity relationship of the ATP-dependent actin-myosin sliding causing cytoplasmic streaming in algal cells, studied using a centrifuge microscope.
When uncoated polystyrene beads suspended in Mg-ATP solution were introduced into the internodal cell of an alga Chara corallina, the beads moved along the actin cables with directions and velocities (30-62 microns s-1) similar to those of native cytoplasmic streaming. Bead movement was inhibited both in the absence of ATP and in the presence of CA2+, as with native cytoplasmic streaming. These results indicate that bead movement is caused by cytoplasmic myosin molecules attached to the head surface interacting with actin cables. The steady-state force-velocity relationship of the actin-myosin sliding that produces cytoplasmic streaming was determined by applying constant centrifugal forces to the beads moving on the actin cables. The force-velocity curve in the positive load region was nearly straight, and the implications of this shape are discussed in connection with the kinetic properties of the actin-myosin interaction in cytoplasmic streaming. It is suggested that the time for which a cytoplasmic myosin head is detached from actin in one cycle of actin-myosin interaction is very short. The Ca(2+)-induced actin-myosin linkages, responsible for the Ca(2+)-induced stoppage of cytoplasmic streaming, were shown to be much stronger than the rigor actin-myosin linkages.
Chaen
S
S
Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan.
Inoue
J
J
Sugi
H
H
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000502:physiology*; D002498:Centrifugation / Q000295:instrumentation / Q000379:methods; D000460:Chlorophyta / Q000166:cytology / Q000502:physiology*; D003595:Cytoplasmic Streaming; D008853:Microscopy / Q000379:methods; D008863:Microspheres; D009218:Myosins / Q000378:metabolism*; D014741:Video Recording
D000199:Actins; D000255:Adenosine Triphosphate; D009218:Myosins