Metabolites and Biomolecules Quiz

Introduction to Enzymes

• Enzyme activity in body fluids is affected by pathological processes.
• Measuring enzyme activity is used for disease investigation.
• Injury or death of tissues releases tissue-specific enzymes into the bloodstream.
• Elevated enzyme levels indicate tissue problems and are used in disease diagnosis.

Measurement of Serum Enzymes

• Enzymes are normally intracellular, with low concentrations in blood.
• Enzyme release (leakage) into the blood indicates cell damage (cell death, hypoxia, intracellular toxicity).
• Quantitative measurement of cell/tissue damage is possible.
• Organ specificity exists, but is not absolute despite similar gene content.
• Enzyme amounts vary in different cells.
• The time course of the disease is relevant.

What to Know

• Enzymes have several main features and properties.
• Coenzymes have specific structures and functions.
• Enzyme kinetics are important.
• Enzyme activity is crucial to understand.

Isoenzymes - General Features

• Isoenzymes (isozymes) are multiple forms of the same enzyme.
• They differ in amino acid sequence.
• They catalyze the same chemical reaction.
• Primary structure differences are genetically determined.
• They may have different subcellular distributions (e.g., cytoplasm vs. mitochondria).

Isoenzymes - General Features (continued)

• Isoenzymes may have different tissue distributions.
• They might be combined from more subunits (quarternary structure).
• Kinetic properties (KM) can vary.
• Isoenzymes are usually determined by electrophoresis.

Proenzyme

• A proenzyme (zymogen) is an inactive form of an enzyme.
• It becomes active after partial proteolysis.
• Pepsinogen (Inactive form) - Pepsin (active form).

Enzymes Routinely Measured

• Aspartate Aminotransferase (AST) / Serum Glutamate-Oxaloacetate Transaminase (SGOT): Present in the heart and liver.
• Alanine Aminotransferase (ALT) / Serum Glutamate-Pyruvate Transaminase (SGPT): Present in the heart and liver.
• Alkaline Phosphatase (ALP): Bone, intestine, other tissues.
• Acid Phosphatase (ACP): Prostate.
• Glutamyl Transferase (GT): Liver
• Creatine kinase (CK): Muscle (including cardiac).
• Lactate Dehydrogenase (LDH): Heart, liver, muscle, RBCs.
• Amylase: Pancreas.

Myocardial Infarction (MI)

• Necrosis of the myocardium (but not angina pectoris) releases CK, AST, and LDH.
• Creatine kinase (CK) activity rises within 6 hours of MI.
• Total CK peaks at 24-36 hours.
• In uncomplicated cases, CK returns to normal within 3 days.
• Serum AST rises more slowly, peaking in 48 hrs and returning to normal in 4-5 days.
• Low LDH elevation within the first 24 hours with maximum elevation around 3 days and lasting up to 8 days.
• Enzymes in general are relatively non-specific to myocardial tissue.

Liver Diseases

• Hepatic necrosis, hepatitis, cholestasis, jaundice, and hepatocellular damage are liver-related problems.
• Serum enzyme assays are helpful for liver and drug-related issues.

Liver Enzymes (ALT, AST, GGT, ALP, LDH):

• ALT is more specific than AST as an indicator of hepatocellular damage.
• Hepatocellular disease primarily affects ALT & GGT to a lesser extent, increasing values by at most three times the normal level.
• Cholestasis, due to a blockage in the liver's bile ducts causes an increase in ALP and GGT.

Alanine aminotransferase (ALT)

• Widely distributed, but largest amounts found in the liver. Present in smaller amounts in the heart (typically normal after MI).
• Congestive cardiac failure can cause release from the liver. More specific to liver disease than AST.

Aspartate aminotransferase (AST)

• Widely distributed in the body.
• Main sources are heart, liver, skeletal muscle, and kidney.
• Useful in diagnosing MI, liver disorders, and muscle damage.
• Causes of high serum AST include hepatitis, hepatic necrosis, cholestasis, myocardial infarction, trauma, crush injury, and myopathy of the skeletal muscles , and hemolysis.

Alkaline Phosphatase (ALP)

• Widely distributed, with high concentrations in intestines, liver, bone, spleen, placenta, and kidney.
• Serum ALP is increased in bone disorders, healing fractures, pregnancy, and hepatobiliary issues (mainly due to cholestasis).
• Decreased levels can be inherited.

Alkaline phosphatase (ALP) (Continued)

• Physiologically increased in infancy, puberty and pregnancy.
• Causes of increased ALP include hyperparathyroidism, osteomalacia, rickets, Paget's disease, osteomyelitis and carcinoma of the bronchus.
• Increased levels in hepatobiliary diseases such as hepatitis, cholestasis and cirrhosis.

Acid phosphatase (ACP)

• Present in prostate, bone, liver, spleen, kidney, and RBCs.
• Primarily used to diagnose prostate cancer but also assessed in other prostate conditions (prostatitis, benign prostatic hypertrophy).
• Also assessed in non-prostatic conditions (hemolysis, Paget's disease, metastatic carcinoma of the breast, Gaucher's disease).
• Prostate-specific antigen (PSA) is an enzyme present in prostatic tissue, and in cases of metastatic carcinoma.

Amylase (AMS)

• Breaks down complex polysaccharides in the body.
• Calcium dependent, metalloenzyme.
• High levels associated with acute pancreatitis and mumps.
• Sources include the pancreas, salivary glands, and intestinal malignancy.
• Clinically helpful for diagnosing and monitoring pancreatitis.

Lipase (LPS)

• Breaks down fats into monoacylglycerol and free fatty acids.
• Primarily found in the pancreas.
• Used to diagnose acute pancreatitis.
• Rises within 1-12 hours of an acute attack, and can remain at elevated levels for several days.
• Compared to amylase, lipase is more specific to acute pancreatitis.

Specificity of Enzymes

• Greater specificity is achieved by considering clinical features and isoenzyme determinations.
• AST elevations can be caused by MI or hepatitis, making LDH levels helpful for diagnosis clarification.
• Differentiating ALP in cholestasis from other conditions relies on differentiating bilirubin and transaminase levels.
• GGT is crucial for confirmation of cholestasis.

Conditions in which level of activity in serum is elevated for various enzymes

(Table)

Isoenzymes Composition

(Tables showing isoenzyme, composition, presence, and elevation)

Creatine Kinase (CK)

• Dimer composed of two different chains (M - muscle, B - brain).
• Three isoenzymes: MM (muscle), MB (heart), BB (brain).
• MM is the major isoenzyme in blood (95%).
• MB is a useful marker for myocardial infarction.
• CK is associated with ATP regeneration in muscle and nervous tissue, and elevated levels indicate MI, muscular dystrophy, and stroke.

Creatine Kinase (CK) (Continued)

• CK occurs in dimer form via two different subunits (M, B) and CK-BB in the brain, CK-MB in cardiac muscle, and CK-MM in muscle.
• CK-MB is released from cardiac muscle cells following MI.

Creatinine

• Most reliable test of glomerular function.
• End product of nitrogen metabolism.
• Changes can occur due to muscle mass changes, surgery, steroid treatment, and refeeding, independently of kidney function.

GFR - Glomerular Filtration Rate

• Reflects the number of functioning glomeruli.
• Estimate of renal impairment.
• Serum sample for U&E's is required.
• Calculated using a formula involving creatinine, age, gender and race factors.
• A useful measure for monitoring chronic kidney disease (CKD) and function.
• It differs from creatinine clearance by being more reliable and removing urine collection errors.

GFR Stages (Table)

• GFR stages with descriptions and treatment.

Cholesterol

• Cholesterol is a fatty substance crucial for cell membranes and hormone production.
• Primarily produced by the liver but also found in certain foods.
• High cholesterol levels can increase the risk of heart disease.

Cholesterol Test (Table)

• Categories of total cholesterol levels and associated heart disease risks.

Genetic Influence

• Some people inherit a higher cholesterol concentration due to impeded excretion from bloodstream.
• This condition is often familial and is also known as familial hyperlipidaemia or familial hypercholesterolemia.

Who Needs Cholesterol Checked

• People with existing heart disease.
• Family history of high cholesterol.
• Diabetes.
• High blood pressure.
• Family history of heart disease.

What Can I Do to Help Myself?

• Reduce total fat intake.
• Swap saturated fats for unsaturated fats (e.g., polyunsaturated and monounsaturated fats).
• Increase fruit and vegetable intake.
• Increase carbohydrate intake for energy.
• Manage weight to recommended levels.

Plasma Proteins

• Plasma contains approximately 7% protein.
• Normal range of total plasma protein is 6.3-8.4 g/dL.
• Primary classes of plasma proteins are Albumins, Globulins(Alpha, Beta, Gamma), Fibrinogen and Other proteins.

Plasma Proteins - Albumin

• Forms 55-60% of total plasma proteins.
• Normal value is 3.5-5.0 g/dL.
• Molecular weight: 66,500 D (smallest).
• Single peptide chain of 585 amino acids.
• Major function: plasma colloid osmotic pressure.
• Transport protein for hormones, drugs and other substances.
• Hypoalbuminemia is associated with liver failure, malnutrition, chronic infection.

Plasma Proteins - Globulin

• Forms approximately 35% of total plasma proteins.
• Normal level is approximately 2-3 g/dL.
• Large variety of globulins like alpha, beta & gamma.
• Important in immune functions and transporting substances.

Fibrinogen

• Forms approximately 4-6% of total plasma proteins.
• Normal range is 0.3-0.4 g/dL.
• Important in blood clotting and contributing to blood viscosity.
• Molecular weight 400,000-500,000 D.

Other Plasma Proteins

• Includes regulatory proteins, hormones, enzymes, and prohormones.
• Represents about 1% of the total plasma proteins.

Methods of Plasma Protein Separation

• Electrophoresis, salting out, ultracentrifugation, affinity chromatography, fractional precipitation, and immune electrophoresis are methods for separating plasma proteins.

Hypoproteinemia

• Causes include liver failure, nephrotic syndrome, malnutrition, malabsorption, severe burns, infection, and genetic factors.

Functions of Plasma Proteins (Summary Table)

Test your knowledge of metabolites, biomolecules, and enzymes. Questions cover primary vs. secondary metabolites, their roles in biological systems, and the clinical significance of enzymes like AST and ALT. Explore key concepts and applications in biochemistry and diagnostics.