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Motility processes in Acantharia. II. A Ca 2+ dependent system of contractile 2–4 nm filaments isolated from demembranated myonemes
Author(s) -
Febvre Jean,
FebvreChevalier Colette
Publication year - 1989
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1111/j.1768-322x.1989.tb00869.x
Subject(s) - biophysics , contraction (grammar) , motility , divalent , biology , calmodulin , muscle contraction , organelle , calcium , biochemistry , microbiology and biotechnology , anatomy , chemistry , organic chemistry , endocrinology , enzyme
Myonemes of the acantharians are contractile ribbon‐like organelles. As previously shown, their motility is based on the coiling mechanism of double‐twisted 2–4 nm nonactin filaments [14]. Myonemes have been isolated and manipulated in vitro . After demembranation, the contraction takes place when the Ca 2+ concentration is above 10 −7 M, whereas relaxation occurs below this threshold concentration. The response to Ca 2+ ions is an on/off mechanism. Both contraction and relaxation can be induced repeatedly without fatigue phenomena. Other divalent cations such as Sr 2+ , Ba 2+ , Ma 2+ , CO 2+ , and La 3+ can replace Ca 2+ in inducing contraction of the demembranated myonemes although with less efficiency. Contraction and relaxation are ATP‐independent and calmodulin is not involved in this in vitro motility process. The myoneme is a strongly resistant structure which is capable of contracting and relaxing under various extreme conditions which indicates very stable proteins and resistant functions.