Journal Article

Effects of Ca<sup>2+</sup> and Calmodulin on the Motile Activity of Characean Myosin In vitro

Jun-ya Awata, Kazuhiro Saitoh, Kiyo Shimada, Taku Kashiyama and Keiichi Yamamoto

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 42, issue 8, pages 828-834
Published in print August 2001 | ISSN: 0032-0781
Published online August 2001 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pce107
Effects of Ca2+ and Calmodulin on the Motile Activity of Characean Myosin In vitro

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It is well known that the cytoplasmic streaming of characean cells is readily inhibited by Ca2+. However, neither the actin-activated MgATPase nor the in vitro motile activity of purified characean myosin were inhibited by Ca2+. 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 Ca2+ is due to the dissociation of some calmodulin molecules from the neck region during the course of protein purification. To determine strictly the Ca2+ 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 Ca2+. The results suggest that the brief cessation of cytoplamic streaming is not caused by the direct inhibition of myosin activity by Ca2+.

Keywords: Key words: Ca2+ — Calmodulin — Chara corallina — Cytoplasmic streaming — Myosin.; Abbreviations: AEBSF, 4-(2-aminoethyl)benzensulfonyl fluoride hydrochloride; CaM, calmodulin; CDPK, calcium-dependent protein kinase; DTT, dithiothreitol; EGTA, O,O′-bis(2-aminoethyl)ethyleneglycol-N,N,N′,N′-tetraacetic acid; MOPS, 3-morpholinopropanesulfonic acid; PMSF, phenylmethylsulfonyl fluoride.

Journal Article.  4902 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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