Key result
Densitometry and in vitro simulation of Gray's mussel catch muscle suggest that myorod, rather than twitchin, is responsible for forming catch load-bearing cross-links due to its high content.
In molluscan catch muscle, myorod rather than twitchin may be responsible for the formation of catch load-bearing cross-links due to its high abundance.
Hypothesis-generating for catch mechanisms; leaves open relevance to mammalian muscle until validated in vivo.
In the work, we performed densitometry of thick filaments of the Gray's mussel catch muscle; densitometry included determination of electrophoretic dye binding constants of proteins. The results of densitometry showed that the content of twitchin in thick filaments is significantly (10 times) lower than the content of myosin. We performed an in vitro simulation of the contractile apparatus of the catch muscle and showed that with such content, links formed by twitchin cannot stop "relaxation". So, we doubt that the role of twitchin in the formation of the catch state is to form load-bearing links between thin and thick filaments that keep the muscle in the contracted state. At the same time, densitometry has shown that the content of the unique catch-muscle protein - myorod - significantly exceeds the content of twitchin and reaches the level of myosin. Like twitchin, myorod is capable of forming regulated cross-links between thick and thin filaments. Such a high content of this protein may indicate that it is myorod, and not twitchin, that is responsible for the formation of catch load-bearing cross-links.
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Vyatchin et al. (2019) studied Molluscan catch muscle physiology. In vitro simulation of the contractile apparatus was evaluated on Protein content of twitchin and myorod in thick filaments. Densitometry and in vitro simulation of Gray's mussel catch muscle suggest that myorod, rather than twitchin, is responsible for forming catch load-bearing cross-links due to its high content.
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