Effects of Ca(2+) and calmodulin on the motile activity of characean myosin in vitro.
It is well known that the cytoplasmic streaming of characean cells is readily inhibited by Ca(2+). However, neither the actin-activated MgATPase nor the in vitro motile activity of purified characean myosin were inhibited by Ca(2+). Recently, amino acid sequence of characean myosin was determined in our laboratory and the sequence revealed that characean myosin contains six calmodulin binding sites in the neck region. We also detected calmodulin in quickly prepared characean myosin fraction. It is, therefore, possible that the insensitivity of characean myosin to Ca(2+) is due to the dissociation of some calmodulin molecules from the neck region during the course of protein purification. To determine strictly the Ca(2+) sensitivity of characean myosin, we intentionally used crude preparation of characean myosin to reduce the possibility of calmodulin dissociation and examined the motile activity of characean myosin in vitro in the presence of excess characean calmodulin. We could not observe any drastic inhibition of characean myosin activity by Ca(2+). The results suggest that the brief cessation of cytoplasmic streaming is not caused by the direct inhibition of myosin activity by Ca(2+).
Awata
J
J
Department of Biology, Faculty of Science, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522 Japan.
Saitoh
K
K
Shimada
K
K
Kashiyama
T
T
Yamamoto
K
K
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000494:pharmacology; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D000460:Chlorophyta / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D004247:DNA / Q000302:isolation & purification; D004926:Escherichia coli; D008969:Molecular Sequence Data; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
D000199:Actins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D004247:DNA; D019703:Calcineurin; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins; D002118:Calcium