Poster: Cytoskeleton: Structure & Function

Abs # 1101: Susceptibility of characean myosin to SH reagents

Presenter:	Seki, Masaya , 98s4021@bio.s.chiba-u.ac.jp
Authors	Seki, Masaya  (A)   Awata, Jun-ya  (A)   Shimada, Kiyo  (B)   Kashiyama, Taku  (C)   Ito, Kohji  (A)   Yamamoto, Keiichi  (A)
Affiliations:	(A): Department of Biology, Chiba University (B): Kazusa DNA Laboratory (C): Pharmacology Department, Juntendo University School of Medicine

Treating plant cells such as Nitella internodal cells with N-ethylmaleimide (NEM) stops cytoplasmic streaming. It has long been believed without proof that the reagent primarily attacks myosin in the flowing cytoplasm assuming that Nitella myosin reacts with NEM similarly to well known skeletal muscle myosin. It was so widely believed that NEM was used to inactivate putative myosin in Nitella cells and the susceptibility of cellular and intracellular motile events in plants to NEM have been regarded as evidences for the involvement of myosins, even though this membrane permeating reagent is known to react nonspecifically with SH-containing proteins. We studied, therefore, susceptibility of characean myosin to NEM. We compared the effect of NEM on the motile and ATPase activities of skeletal muscle myosin with that on myosin prepared from Chara corallina. It was found that the motile activity of myosin prepared from NEM-treated C. corallina decreased to a level accountable for the decrease in the velocity of cytoplasmic streaming but it was also found that Chara myosin was far less susceptible to NEM than skeletal muscle myosin. Because of this low susceptibility, it is clear that chemically modified protein is not myosin alone. Care should be taken to use SH reagents to inactivate motile events in plant.