Key result
Cleavage of actin by trypsin or chymotrypsin produces a protease-resistant core that retains full ATP binding capacity and can refold to functional forms, representing an independent functional unit.
A protease-resistant core of actin functions as an independent unit capable of binding ATP and refolding.
Actin refolding data warrant no clinical changes; leaves open extension to human cardiac actinopathies.
Actin can be cleaved by trypsin or chymotrypsin into a large, autonomous fragment with approximately 80% of the mass of the undegraded polypeptide. The protease-resistant cores obtained with either enzyme are very similar. Although the fragment does not bind calcium ions and fails to polymerize to the filamentous form of actin or to stimulate myosin adenosine triphosphatase (ATP phosphohydrolase, EC 3.6.1.3) activity, it retains the full capacity to bind ATP. This observation suggests that it represents an independent functional unit. Cleavage of globular actin with either trypsin or chymotrypsin occurs with half-times of 3 min, while that of filamentous actin proceeds with reaction half-times of 20 min for trypsin and nearly 2 hr for chymotrypsin. Denaturation and renaturation of the trypsin-resistant core shows that approximately 20% of the molecules refold to functional forms which indicates that the fragment can be considered as an independent unit of folding as well.
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Jacobson et al. (1976) studied this question. Trypsin or chymotrypsin cleavage was evaluated on ATP binding capacity and folding of protease-resistant core of actin. Cleavage of actin by trypsin or chymotrypsin produces a protease-resistant core that retains full ATP binding capacity and can refold to functional forms, representing an independent functional unit.
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