Modifications to scallop heavy meromyosin, such as cross-linking to F-actin or attaching spectroscopic probes, preserve ATPase activity but eliminate calcium sensitivity.
Cross-linking enables Ca2+-insensitive ATPase assays in scallop HMM; leaves open extension to vertebrate cardiac myosins.
Single‐turnover kinetic analysis indicates that scallop heavy meromyosin (HMM) preparations contain a small fraction of unregulated molecules which dominate the steady‐state ATPase activity in the absence of Ca 2+ . This fraction was removed by rapid centrifugation during an effective single turnover of the ATPase in the presence of actin. The maximum ATPase activity of a scallop myosin head was estimated as 10 s −1 by cross‐linking subfragment 1 to F‐actin. HMM became Ca 2+ ‐insensitive during the cross‐linking procedure. Attachment of spectroscopic probes to the reactive thiol group of scallop HMM resulted in the retention of ATPase activity but a loss in Ca 2+ sensitivity.
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Jackson et al. (1986) studied this question.
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