The slow skeletal muscle isoform of myosin shows kinetic features common to smooth and non-muscle myosins

Iorga, Bogdan and Adamek, Nancy and Geeves, Michael A. (2007) The slow skeletal muscle isoform of myosin shows kinetic features common to smooth and non-muscle myosins. Journal of Biological Chemistry, 282 (6). pp. 3559-3570. ISSN 0021-9258 . (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided)

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Fast and slow mammalian muscle myosins differ in the heavy chain sequences (MHC-2, MHC-1) and muscles expressing the two isoforms contract at markedly different velocities. One role of slow skeletal muscles is to maintain posture with low ATP turnover, and MHC-1 expressed in these muscles is identical to heavy chain of the,beta-myosin of cardiac muscle. Few studies have addressed the biochemical kinetic properties of the slow MHC-1 isoform. We report here a detailed analysis of the MHC-1 isoform of the rabbit compared with MHC-2 and focus on the mechanism of ADP release. We show that MHC-1, like some non-muscle myosins, shows a biphasic dissociation of actin-myosin by ATP. Most of the actin-myosin dissociates at up to similar to 1000 s(-1), a very similar rate constant to MHC-2, but 10-15% of the complex must go through a slow isomerization (similar to 20 s(-1)) before ATP can dissociate it. Similar slow isomerizations were seen in the displacement of ADP from actinmyosin(.)ADP and provide evidence of three closely related actinmyosin(.)ADP complexes, a complex in rapid equilibrium with free ADP, a complex from which ADP is released at the rate required to define the maximum shortening velocity of slow muscle fibers (similar to 20 s(-1)), and a third complex that releases ADP too slowly (similar to 6 s(-1)) to be on the main ATPase pathway. The role of these actin-myosin(.)ADP complexes in the mechanochemistry of slow muscle contraction is discussed in relation to the load dependence of ADP release

Item Type: Article
Subjects: Q Science > QH Natural history > QH301 Biology
Divisions: Faculties > Science Technology and Medical Studies > School of Biosciences
Depositing User: Maureen Cook
Date Deposited: 31 Mar 2008 17:43
Last Modified: 28 Apr 2014 15:37
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