Protein Chemistry. Structure, Properties, Research Methods - Shendryk A.N. 2022

Proteins of Blood and Muscle Tissues
Proteins of the Contractile System
Functions of Muscle Tissue Proteins

Skeletal Muscle intracellular Proteins consist of 20–25% Water-soluble sarcoplasmic proteins and water-insoluble myofibrillar proteins. Sarcoplasmic proteins are easily extracted from Muscle tissue with water, a fraction known as myogen. This fraction includes glycolytic Enzymes such as aldolase, glyceraldehyde-3-phosphate dehydrogenase, glycerol-3-phosphate dehydrogenase, and phosphorylase.

Water-insoluble proteins are much more difficult to isolate and obtain in pure form. They can be brought into solution through prolonged extraction with a 0.6 M aqueous potassium chloride solution. When the KCl concentration is decreased, the protein precipitates out again.

Dozens of different contractile proteins have been isolated from the myofibrils of striated muscle, accounting for about 12% of The Cell's dry weight. Among these proteins, Myosin makes up about 55% and Actin about 20%. Other proteins include Tropomyosin at 7%, troponin at 2%, α-actinin at 10%, β-actinin at 2%, C-protein at 2%, and M-protein at 2%. It has now been established that the filamentous, water-insoluble elements of skeletal muscle are formed by three main proteins—myosin, actin, and tropomyosin B—which account for 90% of their mass. These three Proteins can be extracted selectively from muscle. First, myosin is extracted from myogen-free muscle using a cold alkaline 0.6 M KCl solution. Next, actin can be extracted from the remaining muscle tissue with slightly alkalinized cold water. This form of actin is called G-actin, and its molecule has a globular shape. Subsequent extraction of the residue at a elevated Temperature yields tropomyosin B.