Key result
Mns labeling of cardiac myosin without divalent metal ions alters lysyl incorporation, suggesting conformational changes.
The study demonstrates that divalent metal ions induce conformational changes in pig cardiac myosin, altering the accessibility of specific lysyl residues to fluorescent labeling.
No clinical implications for cardiac care; leaves open further structural studies of myosin in animal models.
Two mol of N-methyl-2-anilino-6-naphthalenesulfonyl (Mns) groups was preferentially incorporated into pig cardiac myosin in the absence of divalent metal ions, 1 mol rapidly and 1 mol slowly. In the presence of divalent metal ions. 1 mol was rapidly incorporated but subsequent incorporation was strongly suppressed. No substantial effect of incorporation of Mns groups in the presence or absence of divalent metal ions on the Ca2+- and K+-ATPase activities of myosin was found. However, the fluorescence spectra due to attached Mns groups were different in the two cases. Extensive pronase digestion of labeled myosin indicated that the Mns groups were attached predominantly to lysyl residues, regardless of the labeling conditions. Peptide mapping of the labeled myosin digested with subtilisin, pepsin or trypsin uniformly showed the selective incorporation of an Mns group into essentially one species of peptide. However, the peptide labeled in the absence of divalent metal ions was clearly different from that labeled in their presence. The present results confirm that pig cardiac myosin heavy chains contain two distinct lysyl residues, which are both accessible to labeling with Mns groups only when divalent metal ions are absent. The results also suggest that conformational changes occur around these residues when divalent metal ions are added.
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Hiratsuka et al. (1980) studied this question. N-methyl-2-anilino-6-naphthalenesulfonyl (Mns) labeling vs. Presence vs absence of divalent metal ions was evaluated on Incorporation of Mns groups into pig cardiac myosin and effect on ATPase activities. Labeling of pig cardiac myosin with Mns groups showed preferential incorporation into two distinct lysyl residues in the absence of divalent metal ions, suggesting conformational changes upon ion addition.
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