Muscle protein breakdown can be measured using mass spectrometers. Advances in mass spectrometers have led to increased sensitivity and stability, allowing 단백질 보충제 researchers to measure MPS and MPB over 30 to 45-minute time periods. However, muscle protein breakdown has lagged behind MPS in technical development.
Myofibrillar proteins are the muscle protein building blocks and play an important role in muscle growth and development. The protein is made up of two types: slow and fast. Both types have different sensitivity to pH, temperature and external factors. As such, it is important to carefully adjust the meat processing conditions to maintain the desired functionalities of myofibrillar proteins. This can ensure uniform quality of final muscle food.
The WHC of myofibrillar proteins is governed by the large amount of acidic amino acids like glutamic acid and aspartic acid. These two types of amino acids are responsible for the unique structural properties of myofibrillar proteins. This property enables them to function in a wide range of physiological settings.
Once the rigor mortis process has been completed, the muscle protein’s ionic strength doubles. From 270-300 mosmoles, it reaches 500-600 mosmoles. This increase in ionic strength promotes the activity of muscle proteases and decreases pH.
Postmortem proteolysis affects muscle ultrastructure in a variety of ways. Actin and myosin are minimally affected by this process, but cytoskeleton proteins are more affected. These changes in muscle protein quality affect meat tenderness. In addition to altering the ultrastructure of myofibrils, postmortem proteolysis can lead to transverse myofibril rupture. The protein fragments that are ruptured in the muscle tissue contain actin, titin, and nebulin.
Myofibrillar proteins are composed of two heavy polypeptide chains and four light polypeptide chains. Myosin is the most abundant myofibrillar protein. Its structure and function depend on the type of myosin.
Mechanisms of muscle protein breakdown
Muscle protein breakdown results in the reduction of myofiber size and the loss of proteins, organelles, and cytoplasm. The process is controlled by several pathways and transcription factors, including the ubiquitin-proteasome system and the autophagy-lysosome pathway. Muscle protein breakdown is a normal part of muscle building and a critical step in the process.
A key process in muscle protein breakdown involves the activation of the autophagy system, which helps to destroy intracellular organelles and target proteins. Autophagy is triggered by several stressors, including starvation and the production of reactive oxygen species. Various factors can trigger autophagy, including muscle injury, but not all can trigger the process.
The mTOR pathway is an important pathway involved in muscle protein synthesis. However, it should be noted that blocking mTOR can cause muscle atrophy. It is also important to note that these signals are important in stress response pathways, which affect gene transcription. In addition, amino acids play an important role in the regulation of gene transcription in the catabolic state. They also play a role in maintaining muscle homeostasis.
The main protein degradation systems in the body are the autophagy system, the UPP system, and the calpain system. Though there is limited data from human studies to assess how these systems work together, these three systems play a crucial role in MPB. However, in animal models, the UPP and the calpain systems appear to be more important. In addition, autophagy seems to play a critical role in the degradation of receptor proteins at the membrane, which is a crucial factor in muscle remodeling.
Effects of protein ingestion with exercise on skeletal muscle protein
Studies have shown that muscle protein synthesis and breakdown rates increase during exercise, and that protein ingestion after exercise improves muscle protein balance. However, if the muscle is not adequately reconditioned and protein intake is not sufficient, the net protein balance remains negative. This means that proper nutrition is necessary for optimal muscle hypertrophy and reconditioning.
Intake of protein before exercise promotes the early recovery from intense exercise. It has been shown that exhaustive exercise causes redistribution of blood to skeletal muscle tissue, which can impair protein digestion and absorption kinetics. This may increase the availability of amino acids during exercise, and dietary protein may help facilitate the process.
Protein ingestion before and after resistance-type exercise increases post-exercise muscle protein synthesis rates. It also enhances the skeletal muscle adaptive response to training, resulting in greater gains in skeletal muscle mass and strength. Despite these promising results, however, many studies have not been able to detect a surplus benefit of dietary protein supplementation. It remains to be seen how much supplementation may be beneficial for muscle recovery and performance.
Compared to 20 g protein, the 40-g dose of protein elicited a 20% higher MPS response in exercised muscles. These results suggest that a higher protein intake is required for whole-body resistance-type exercise, and for a more direct comparison. However, the results also suggest that the MPS response is transient. However, if exercise-induced anabolic sensitivity is enhanced in the exercised muscle, the MPS response may be prolonged.