Proteins and Amino Acids
Proteins and Amino Acids
Definition of Proteins
Proteins are formed by different arrangements of amino acids.
A short chain of amino acids is referred to as a peptide.
A larger chain of amino acids is classified as a protein.
There are only 20 amino acids that comprise all the proteins in a mammal's body.
Structure of Proteins
Primary Structure
The linear arrangement of amino acids is termed the primary structure.
Secondary Structure
As amino acids build upon one another, they can form the secondary structure.
This refers to the initial folding of amino acid chains into structural motifs, such as alpha-helices and beta-pleated sheets.
Tertiary Structure
The tertiary structure refers to the overall three-dimensional shape of a protein that results from interactions between the side chains of the amino acids.
Quaternary Structure
The quaternary structure involves the interaction of multiple polypeptide chains (subunits) to form a functional protein complex.
Not all proteins have a quaternary structure; it primarily applies to proteins composed of more than one polypeptide.
Protein Complexity
As proteins increase in complexity, they may also have carbohydrates or lipids attached:
Glycoproteins: Formed by the combination of protein and carbohydrate.
Lipoproteins: Formed by the combination of protein and lipid.
Types of Protein Structures
Proteins, once in their tertiary or quaternary structures, can be classified as either:
Globular Proteins: Typically spherical and soluble in water.
Fibrous Proteins: Typically elongated and insoluble in water, providing structural support.
Functions of Proteins
A) Globular Proteins
Functions include:
Hormones: Act as “messengers in the body” inducing chemical changes (e.g., Insulin).
Enzymes: Catalysts that “speed up” chemical reactions in the body, relevant in digestion and tissue repair (e.g., Lipase).
Receptors: Proteins that receive signals within the body and trigger responses.
Antibodies: Immunoglobulins that play a role in the immune response, acting as defenders (e.g., responding to vaccinations).
B) Fibrous Proteins
Functions include:
Binding together cells and tissues.
Major examples:
Keratin: Found in nails and fur.
Collagen: Found in bones and cartilage.
Contractile Proteins: Present within muscle tissue.
Amino Acids
Non-Essential Amino Acids
These amino acids are produced by the mammalian body and are not required to be obtained through the diet.
Essential Amino Acids
These amino acids must be obtained through diet, as the body cannot synthesize them. Examples include:
Leucine
Taurine
Arginine
Specific deficiencies to note:
Taurine deficiency in cats.
Methionine deficiency in dogs.
Protein Analysis
Total Protein Evaluation
Total protein (TP) can be evaluated using either:
Large machine analyzers
Simple refractometry
Key Types of Blood Proteins
Albumin: Comprises 50-60% of the protein in plasma.
Globulins: Involved in immune defense.
Evaluation using Blood Chemistry Screen Analyzer
The formula used: Total Protein (TP) = Albumin + Globulins.
Sample Collection: Utilize a red top or serum separator tube.
Plasma Proteins – Albumin
Produced in the liver.
Major role in maintaining osmotic pressure in plasma, helping to keep water in blood vessels.
Functions as a carrier protein for substances like unconjugated bilirubin.
Hyperalbuminemia
An increase in albumin levels in the blood is often a result of:
Physiological Hemoconcentration: Caused by dehydration; results in elevated albumin and globulins.
False Increase: Can occur from lipemic or hemolyzed samples.
Actual Increase: May occur when more albumin is produced by the liver than normal.
Hemoconcentration: Involves elevated levels of hemoglobin, hematocrit, and plasma protein.
Hypoalbuminemia
Common Causes Include:
Hemodilution: Overloading fluids leading to low total protein.
Decreased Production: Significant liver damage (>80% damage).
Increased Loss: Due to conditions affecting the kidneys (Protein Losing Nephropathy, PLN) or gastrointestinal tract (Protein Losing Enteropathies, PLE), such as inflammatory bowel disease.
Catabolism: Resulting from chronic malnutrition, where a lack of available amino acids reduces albumin production.
Globulins
Related to immune defense functions.
Gamma Globulins
Involves immunoglobulins: IgM, IgA, IgG, IgD, IgE; these are antibodies essential for immune responses.
Hypoglobulinemia
Example: Failure of passive transfer, where newborns fail to receive maternal colostrum and antibodies, thereby compromising their immune system and ability to fend off infections.
Hyperglobulinemia
Often results from increased production of antibodies in response to various stimuli (e.g., chronic skin disease).
Enzymes: Role and Importance
Description of Enzymes
Enzymes are proteins that act as biological catalysts. They “speed up” chemical reactions in biological processes including:
Digestion
Tissue repair (e.g., Lipase)
Common Enzymes Monitored in Chemistry Panels
Liver Enzymes:
ALT: Most liver-specific; increases indicate liver disease.
AST: Indicates liver, skeletal muscle cell damage, or red cell damage.
GGT: Helpful in diagnosing liver disease particularly in horses; more specific in dogs and cats.
ALKP: Elevated in liver disorders, particularly cholestasis; may also reflect bone growth.
Muscle Enzyme:
Creatine Kinase (CK): Associated with muscle and heart health; an increase can indicate muscle damage or heart disease.
Pancreatic Enzymes:
Amylase: Non-specific; may elevate due to renal disease.
Lipase: Also non-specific and can indicate GI disease; however, pancreas-specific lipase tests help diagnose pancreatic diseases like pancreatitis.
General Guidelines for Enzyme Testing
Serum, not plasma, is preferred (using red top tubes or STT tubes).
Consult lab protocols for specific tests that may require unique collection methods or conditions.
Conclusion
Understanding the roles and measurements of proteins and enzymes is fundamental for assessing animal health, diagnosing diseases, and formulating treatment plans.