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Twelve peptide analogs of the actomyosin ATPase inhibitory region of rabbit skeletal troponin I (Tn-I) have been synthesized by the solid phase method and tested for biological activity in both actomyosin and acto-S1(A1) systems. Acto-S1(A1) is a cleaner and more facile system and we found no important discrepancies in the results for the two systems. These studies indicate that the sequence 105 to 114 is necessary for inhibition and that the inhibition is on the order of that reported for the 21-residue cyanogen bromide fragment of Tn-I (residues 96 to 116). We have shown the importance of lysine 105 and that of a bulky side chain at position 114 to this inhibition. Both the high activity of peptides containing the sequence 105 to 114 compared to Tn-I (45% on a molar basis) and the previously demonstrated tropomyosin specificity of this activity indicate that the relative inhibitory activity of these peptides is applicable to the discussion of the inhibitory activity of Tn-I. We have proven that actin concentration is a significant factor determining the extent of inhibition of both Tn-I and the peptides. We have also established that the charges on alpha-amino and alpha-carboxyl groups of a peptide, which do not appear in the parent protein, can modify the activity of the peptides. This must be taken into account when extrapolating from the activity of a peptide to the activity of the protein.
Talbot et al. (Sun,) studied this question.