Interaction of tropomyosin with troponin components.

1. The TN-T and TN-I components of troponin both interact with tropomyosin and cause its precipitation in 0.1 M KC1 at neutral pH. The precipitate contains both end-to-end and side-by-side aggregates of tropomyosin molecules. 2. The TN-T and TN-I components change the band pattern of tropomyosin paracrystals formed in MgC1(2) solutions, although in different ways. TN-T causes the formation of hexagonal net structures, double-stranded net or paracrystals which result from the collapse of the double-stranded net. TN-I at pH 7.9 causes the formation of paracrystals with a 400 A periodic band pattern and a 200 A repeat. The same band pattern can also be seen in tropomyosin paracrystals formed at pH values below 6.0. 3. The TN-C component does not precipitate tropomyosin in 0.1 M KC1. The aggregates of tropomyosin obtained with either TN-T or TN-I can be solubilized by the addition of TN-C. No interaction of TN-C was observed with tropomyosin paracrystals formed in the presence of MgC12.