2004
DOI: 10.1074/jbc.m405191200
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Protein Phosphatase 2B Dephosphorylates Twitchin, Initiating the Catch State of Invertebrate Smooth Muscle

Abstract: "Catch" is the state where some invertebrate muscles sustain high tension for long periods at low ATP hydrolysis rates. Physiological studies using muscle fibers have not yet fully provided the details of the initiation process of the catch state. The process was extensively studied by using an in vitro reconstitution assay with several phosphatase inhibitors. Actin filaments bound to thick filaments pretreated with the soluble protein fraction of muscle homogenate and Ca 2؉ (catch treatment) in the presence o… Show more

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Cited by 36 publications
(21 citation statements)
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References 28 publications
(56 reference statements)
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“…As suggested previously (11), the formation of the high force state is thought to displace the twitchin interactions with myosin and actin and thus prevent formation of catch. This is consistent with observations made with reconstituted fibers (18). Thus, during an active contraction, the competition between the actin-myosin interaction sites and the sites on actin subdomain I and on myosin loop 2 for twitchin would be lessened by formation of the high force state.…”
Section: Discussionsupporting
confidence: 91%
“…As suggested previously (11), the formation of the high force state is thought to displace the twitchin interactions with myosin and actin and thus prevent formation of catch. This is consistent with observations made with reconstituted fibers (18). Thus, during an active contraction, the competition between the actin-myosin interaction sites and the sites on actin subdomain I and on myosin loop 2 for twitchin would be lessened by formation of the high force state.…”
Section: Discussionsupporting
confidence: 91%
“…However, this is unlikely in view of a very recent finding that the Ca 2+ -dependent protein phosphatase 2B is involved in dephosphorylation of twitchin [52]. In our experiments, [Ca 2+ ] was below 10 À8 M when cAMP was added so that the activity of this phosphatase is presumably very low under our experimental conditions.…”
Section: Parametermentioning
confidence: 53%
“…It should be emphasized that a direct role for Ca 2+ in binding of the D2 peptide to either actin or myosin is not suggested and there is no evidence from our data to implicate a Ca 2+ sensitive step, other than the regulation of actin-activated ATPase by Ca 2+ binding to myosin. Dephosphorylation of twitchin by calcineurin (Castellani and Cohen, 1992;Yamada et al, 2004) would be coincident with initiation of contraction since both events are Ca 2+ dependent, and thus for most of the contractile phase twitchin is dephosphorylated and theoretically (Siegman et al, 1998). A competition between twitchin and myosin might explain the in vitro inhibition of Mg 2+ ATPase activity of actomyosin by relatively high concentrations of TWD2-S.…”
Section: Discussionmentioning
confidence: 99%