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Microscopic observations on the interaction of heavy meromyosin-S-1 and actin in myofibrils
Abstract:
The binding of the proteolytic myosin fragment, HMM-S-1, to the non-overlapping part of actin filaments in intact myofibrils can be demonstrated under the phase contrast microscope as a contrast reversal of striation. The same effect can be seen on ghost myofibrils (after myosin extraction) where the whole length of the I-filaments is bare. HMM-S-1-loaded ghost myofibrils contracted upon addition of ATP in agrement with the recent report of Oplatka et al. (1974a, b) but under the same conditions ghost myofibrils not treated with HMM-S-1) also contracted. If the ghosts were prepared under conditions more favourable to myosin extraction, contraction became nil or negligible even when we loaded then ghosts with S-1. Thus we attribute the effect described by Oplatka's group to a small numer of residual myosin filaments in the ghosts.
Insights
Myosin fragment HMM-S-1 binding to actin filaments causes contrast reversal. However, observed contraction in ghost myofibrils was attributed to residual myosin, not the added fragment.
Area of Science:
- Muscle physiology
- Biochemistry
- Cell biology
Background:
- Myosin fragment HMM-S-1 binding to actin filaments is visualized via contrast reversal in myofibrils.
- Ghost myofibrils, after myosin extraction, reveal bare I-filaments.
Purpose of the Study:
- To investigate the contraction of ghost myofibrils upon addition of ATP after treatment with HMM-S-1.
- To clarify the mechanism behind observed contractions in ghost myofibrils, particularly in relation to Oplatka et al.'s findings.
Main Methods:
- Utilizing phase contrast microscopy to observe HMM-S-1 binding to myofibrils.
- Preparing ghost myofibrils with varying degrees of myosin extraction.
- Assessing myofibril contraction in response to ATP addition after HMM-S-1 treatment.
Main Results:
- HMM-S-1 binding induced contrast reversal in intact and ghost myofibrils.
- HMM-S-1-loaded ghost myofibrils showed contraction with ATP, consistent with prior reports.
- Unloaded ghost myofibrils also contracted, and contraction diminished with increased myosin extraction, even with S-1 loading.
Conclusions:
- The observed contraction in ghost myofibrils by Oplatka's group is likely due to residual myosin filaments.
- The HMM-S-1 fragment itself may not be the primary driver of contraction in these experimental conditions.