AA Synthesis

Amino Acid Pool and Sources

• In a fed state:

  • Amino acids are primarily sourced from dietary protein.

• In a fasted state:

  • Amino acids derive from the breakdown of body proteins.

• There are two primary sources of amino acids:

  • Dietary protein digestion and absorption: All amino acids from the diet contribute to the amino acid pool if caloric needs and the full spectrum of amino acids are available.

  • Cellular recycling: Body proteins can be broken down for amino acids during fasting or when needed.

Dietary Amino Acids

• If caloric needs and amino acids are fulfilled:

  • Body can synthesize all proteins as dictated by gene expression.

• Example:

  • During the night, the body can utilize amino acids from tissue instead of awakening to eat.

Cellular Mechanisms and Amino Acid Availability

• Every cell has cleanup mechanisms to turnover enzymes and amino acids, maintaining a small cellular pool of amino acids.

  • This pool can met immediate demands for gene expression in the first few hours of fasting.

• Cortisol spikes occur after 4-7 hours of fasting, signaling:
  1. Increased proteolysis in muscle.
  2. Supply of amino acids to other tissues in need.

• If amino acids are present and caloric needs met, the body will produce all necessary nitrogen-containing compounds.

Amino Acid Utilization

• Amino acids can be utilized for:

  • Anabolic reactions

  • Deamination: Removal of nitrogen, converting amino acids into a usable form.

  • Excess nitrogen can be toxic, producing ammonia (NH₃).

• Ammonia is converted into urea in the liver and kidneys, which is excreted in urine.

  • Noticeable changes in urine color and smell indicate urea concentration.

Energy State Influence on Amino Acid Utilization

• Energy state influences how amino acids are used:

  • Adequate caloric intake:

  • Insulin signals tissues to use amino acids for necessary functions, shifting focus to growth and repair.

  • Caloric deficit:

  • Increased oxidation of amino acids to meet energy demands, supporting processes like gluconeogenesis.

  • Low carbohydrate intake leads to amino acids being utilized to maintain blood glucose levels.

Importance of Carbohydrate Intake

• Carbohydrate intake is crucial:

  • Inadequate carbohydrates lead to increased amino acid use in gluconeogenesis to protect blood glucose levels.

  • Adequate energy allows for optimal anabolic processes and protein synthesis.

Protein Quality and Amino Acid Requirements

• High-quality proteins (e.g., animal sources, complementary vegetarian sources) provide essential amino acids:

  • Lack of specific essential amino acids increases chances of amino acids being oxidized or synthesized into lipids.

• Consumption versus requirement:

  • Excessive protein beyond needs can lead to oxidation or conversion to glucose/fats,

  • Energy demands for creating fats from protein are higher than from carbohydrates.

Physiological Influences on Amino Acid Utilization

• Growth and developmental periods (e.g., adolescence, pregnancy) increase amino acid requirements for synthesis and repair.

• Trauma or illness increases demand but reduces efficiency of amino acid utilization.

  • Cortisol plays a significant role in these states, potentially conflict with anabolic processes.

Excess Protein Intake and Health Risks

• Excessive protein intake is linked to:

  • Increased risk of obesity and cardiovascular disease (often associated with high saturated fat from animal proteins).

  • Potential for calcium loss and kidney damage in individuals with preexisting kidney conditions.

  • Increased risk of cancers, particularly colon cancer due to fatty acids and secondary bile acids from high protein consumption.

Amino Acid Functions and Uses

• All amino acids contribute to various functions:

  • Protein synthesis

  • Producing hormones, neurotransmitters, immunoglobulins, etc.

  • Increased protein demands arise during infections, leading to increased immunoglobulin production (e.g., IgA, IgG).

Essential vs Non-Essential Amino Acids

• Essential amino acids must be obtained through the diet:

  • Specific functions tied to key compounds (e.g., tryptophan for serotonin, phenylalanine for tyrosine).

• Non-essential amino acids are generally synthesized from glucose:

  • Formed through metabolic pathways such as glycolysis and citric acid cycle.

• Conditionally essential amino acids, such as tyrosine, derived from phenylalanine, are synthesized based on supply.

Fate of Amino Acids

• After deamination, the carbon skeleton can:

  • Contribute to gluconeogenesis or ketone production.

  • Excess nitrogen must be detoxified into urea via the urea cycle.

• Key players in urea synthesis are aspartate, glutamine, and glutamate.

Proteolysis and Nitrogen Excretion

• During fasting states, proteolysis occurs to supply amino acids for bodily functions.

  • Hormonal support comes from cortisol and glucagon.

• The balance of nitrogen excretion varies:

  • Increases with fasting and decreased as the body adapts to relying on ketone bodies for energy.

Nutrition and Maintenance of Nitrogen Balance

• Nitrogen balance shifts based on protein intake and physiological status:

  • Positive nitrogen balance achieved through sufficiently high protein intake.

  • Negative nitrogen balance results from inadequate intake and excessive muscle breakdown.

Conclusion and Key Takeaways

• Ensuring adequate protein intake to meet gene expression needs is crucial for whole-body maintenance and function.

  • Focus on the quality of protein and the balance of macronutrients to optimize health and bodily functions.

  • Monitoring individual dietary needs can help tailor protein intake for distinct physiological states and health conditions.