Principles of Protein Structure - G. Schultz 1982

Structural Foundations of the Mechanism, Action, and Function of Proteins
Skeletal Muscle: A system in which protein action can be linked to the overall activity of the organ
Conclusion

Cell/13.html">Protein Structure analysis is the primary step in investigating its MECHANISM OF ACTION and, ultimately, its biological function. Currently, the Functions of Hemoglobin and Chymotrypsin are the best understood. The high rate and catalytic efficiency of chymotrypsin (and Other Enzymes) can be attributed to multiple effects that accelerate Chemical Reactions in model systems. These effects include the orientation of substrate(s) within the enzyme's Active Site into a conformation optimal for the reaction, stabilization of reactive groups in the substrate relative to their Transition State, and Acid-Base Catalysis. The energy required for rate acceleration appears to be derived from the Free energy of enzyme-substrate complex formation.

Certain Properties of Proteins can only be explained in light of their function, i.e., their contribution to more complex biological activities. Skeletal Muscle is one of the few systems for which a clear correlation has been established between protein function and organ function. Muscle Cells are activated by nerve impulses (membrane-directed signals). At THE MOLECULAR LEVEL, Muscle contraction relies on the cyclic formation of cross-bridges driven by periodic interactions among Myosin, Actin, and Mg-ATP. Ca²⁺ ions and calcium-binding proteins act as intermediaries between nerve impulses and effectors. This Ca²⁺-mediated signaling limits the response time for on-off switches and prevents unsignaled contractions. In contrast, individual oscillations in the flight Muscles of winged insects are controlled not by Ca²⁺ ions or similar low-molecular-weight compounds, but by the contractile proteins themselves. This enables extremely rapid rhythmic contractions that, once initiated (by Ca²⁺ ions), proceed autonomously. In Conclusion, studies on Muscle tissue clearly demonstrate that protein function bridges the gap between molecular architecture and whole-Organism physiology.