Biological Chemistry - Berezov, T. T., Korovkin, B. F. 1998

Muscle Tissue
Changes in the chemical composition of muscle tissue during ontogenesis

In terms of chemical composition, embryonic Muscle tissue differs significantly from the skeletal musculature of adult organisms. Embryonic Muscles contain more Water than functionally mature muscle tissue. Consequently, the total protein content in embryonic muscle tissue, calculated per wet weight, is lower than that in muscles of animals of the same species during Postnatal development. Compared to adult muscles, functionally immature muscle exhibits a lower content of myofibrillar Proteins (Myosin and Actomyosin) and a higher content of stromal proteins, myoalbumin, and globulins. As the fetus develops, The amount of myofibrillar proteins increases, along with a rise in ATPase activity in muscle extracts.

Embryonic muscle tissue is characterized by a high content of Nucleoproteins, as well as RNA and DNA. As the embryo develops, the levels of nucleoproteins and Nucleic Acids in the muscle tissue rapidly decline. High-energy compounds (ATP and creatine phosphate) are significantly less abundant in functionally immature muscle than in the muscles of mature individuals. Imidazole-containing dipeptides (anserine and carnosine) appear in muscle tissue during a strictly defined period of ontogenesis. The Emergence of these dipeptides is closely linked to Muscle Function and coincides with The formation of the reflex arc that enables motor Reflexes, the onset of Ca²⁺ sensitivity in actomyosin, and the activation of ion pumps. There are also distinct characteristics in the enzyme and isoenzyme profiles of embryonic muscle tissue. For instance, studies have shown that the LDH isoenzyme profile shifts during ontogenesis. In extracts from the skeletal muscles of a 3–5-month-old fetus, LDH₃ and LDH₂ Isoenzymes account for 40% and 31% of total LDH activity, respectively. Over the course of embryonic development, skeletal musculature experiences a gradual increase in The activity of cathodic LDH isoenzymes and a decrease in anodic ones, with the result that in adult Skeletal Muscle, the LDH₅ and LDH₄ isoenzymes exhibit the highest activity. The hexokinase isoenzyme profile in muscle tissue also changes during fetal development: the activity of hexokinase isoenzyme I increases, while that of isoenzyme II decreases. These data regarding changes in The chemical composition of muscle tissue during ontogenesis pertain almost exclusively to skeletal musculature.