Control of tension development in scallop muscle fibres with foreign regulatory light chains.

We have shown previously that chemically skinned fibre bundles from scallop muscle can be desensitized to the action of calcium by the removal of the regulatory light chains of myosin and that sensitivity can be restored by the re-addition of scallop light chains. We have now confirmed these results and extended our observations to fibre bundles from which one or both of the regulatory light chains per myosin have been removed (by treatment with EDTA at 7 and 25 degrees C, respectively) and replaced by the corresponding light chains from other species. In the case of a double substitution--where both light chains were replaced--sensitivity was restored completely by light chains from other molluscs and from gizzard muscle; for a single substitution there was restoration of sensitivity by all the light chains tested.