clinical biochemistry chapter 6- amino acids and proteins

Lipoprotein

Prosthetic Group: Lipid

Glycoprotein

Prosthetic Group: Carbohydrate (< 4 %)

Mucoprotein

Prosthetic Group: Carbohydrate (> 4 %)

Metalloprotein

Prosthetic Group: Metal

Nucleoprotein

Prosthetic Group: DNA, RNA

Phosphoprotein

Prosthetic Group: Phosphate

functions of proteins

1. Control extracellular fluid distribution (colloidal pressure)

2. Play a role in specific immunity (antibodies)

3. Complement activation (complement proteins)

4. Transportation (hormones, drugs, lipids, vitamins, metals)

5. Hemostasis (blood clotting factors)

6. Provide crucial nutrients 

7. Buffering (involved in maintaining body pH)

8. Serve as essential enzymes

9. Production of protein hormones

turnover

a process similar to digestion, proteins within living cells are constantly being degraded and re-synthesized, Ammonia is a byproduct

Oncotic pressure

 One of the most significant functions of plasma proteins, These proteins prevent the loss of fluid into the tissues from the plasma into the tissues. Large proteins cannot cross through the capillary walls and their presence maintains an oncotic pressure which pulls fluid. If there is a significant reduction in plasma proteins, this will reduce the oncotic pressure and result in edema, albumin is mainly responsible

Decreased total protein values can be found due to…

low levels of albumin (hypoalbuminemia). In addition, a profound immunoglobulin deficiency (hypoglobulinemia), traumatic blood loss, nephrotic syndrome (large amount of protein are excreted in the urine), and extensive burns.

Increased total protein values are most often found due to…

decrease in water (dehydration), excessive production of immunoglobulins (hyperglobulinemia), as occurs in multiple myeloma

Biuret Method

the most common procedure used to measure total serum or plasma protein. an alkaline copper sulfate solution forms a colored chelate between the copper ions and two or more adjacent peptide bonds of the proteins. The absorbance of the colored product is measured at 540 nanometers. Amount of light absorbed is directly proportional to the color produced, which in turn is proportional to the number of peptide bonds

Kjeldahl Method

the reference method used to validate other total protein methods. It is a very involved procedure and not practical for most clinical labs

Serum protein electrophoresis (SPE)

a procedure that separates proteins based on their charge and size

Sources of error of serum protein electrophoresis (SPE)

electroendosmosis, the use of plasma as a sample, instead of serum (fibrinogen), hemolyzed samples

Albumin

comprises more than half of the total proteins. Its primary function is to maintain osmotic pressure. also serves as a transport molecule for less soluble substances like fatty acids, bilirubin, hormones, calcium, metals, drugs and vitamins.

Hypoalbuminemia

decreased albumin below the normal reference range. This condition usually leads to tissue edema due to water accumulation in those tissues

hyperalbuminemia

Increased levels of albumin, usually occurs in dehydration or in those receiving albumin therapy. Minor illnesses or changes in posture can change levels by 5 - 10 mg/dL either up or down.

Prealbumin

Its major function is to transport thyroid hormones. In addition, levels fall rapidly if caloric and protein intake decreases; therefore it is sometimes measured as a sensitive indicator of nutritional status because of its very short half-life. usually not visible on gel, can be quantitated using RID, EIA or nephelometry

Proteins included in the alpha- and alpha-2 fractions

increase when there is acute, active tissue damage, While not specific to a particular disease, their levels can be used to monitor treatment. These proteins can be found in:

• Inflammatory conditions

• Malignancy

• Trauma

• Post-operative period

• Autoimmune disease

• Myocardial infarction

Alpha-1 –antitrypsin

is activated by substances released by neutrophils in areas of inflammation. An inherited deficiency of this globulin has been associated with emphysema and cirrhosis. It accounts for 90% of the alpha-1 band and can be quantitated using nephelometry

Alpha-1-acid glycoprotein

This protein may be used to monitor an APR reaction in inflammatory states. Methods used to quantify this protein include RID and nephelometry. Decreased levels are occasionally seen in women taking oral contraceptives.

Alpha-1-fetoprotein (AFP)

a fetal protein that when measured in amniotic fluid and maternal serum is of use in the diagnosis of neural tube defects (open spina bifida, anencephaly). may be seen in persons with hepatocellular carcinoma and other malignancies. Methods used to measure this alpha protein include RIA and EIA.

Alpha-2-macroglobulin

elevated in nephrotic syndrome where smaller proteins are lost and this large protein is retained. Decreases may be seen in rheumatoid arthritis and multiple myeloma. Methods used to measure alpha-2-macroglobulin include RID and nephelometry.

Haptoglobin

a protein that binds free hemoglobin (Hb) intravascularly to facilitate the clearance of the hemoglobin(Hb). Decreases in haptoglobin are associated with hemolytic conditions where relatively large amounts of hemoglobin are released. is also an APR that is increased in inflammatory conditions. Methods used to measure haptoglobin include RID and nephelometry.

Ceruloplasmin

the primary copper-containing protein of plasma, n APR that is increased in pregnancy and during estrogen therapy. Reduced levels may be seen in Wilson's disease

Transferrin

the principle plasma iron transport protein carrying iron from the liver to sites of RBC production in the bone marrow, useful in the differential diagnosis of anemia and for monitoring therapy in iron deficiencies. In addition, it has been called a negative APR because it decreases during inflammation. increases may be seen in iron deficiency, pregnancy, and estrogen therapy. This protein can be measured directly with nephelometry or indirectly as total iron binding capacity (TIBC).

Beta-2-microglobulin (B2M)

used to assess renal tubular function, especially in transplant patients as an early indicator of rejection. Increases are seen in inflammation and neoplasias (especially B cell). The method of measurement for this protein is usually RIA.

Fibrinogen

is decreased in incidences of intravascular coagulation, such as DIC, due to consumption of factors during the coagulation cascade.  This protein is increased during inflammation and tissue injury (a positive APR protein), with increased estrogen (in estrogen therapy or pregnancy), and in renal disease, not found in serum

C-reactive protein (CRP)

an APR present in serum of acutely ill patients, useful for following  the progression and resolution of inflammation, found in myocardial infarction, trauma, surgery, or neoplasm.  CRP is most often measured by RID, nephelometry, and RIA

Multiple myeloma (MM)

a monoclonal gammopathy and is usually a  single immunoglobulin or immunoglobulin chain produced in excessive amounts, creates a sharp monoclonal spike (sharp peak or band) in the gamma region called an M protein

Cryoglobulins

gamma globulins that precipitate in the cold and redissolve when warmed to body temperature. These proteins may be seen in gammopathies, leukemias, systemic lupus erythematosus, rheumatoid arthritis, and inflammatory diseases

Waldenstrom's macroglobulinemia

monoclonal disorder but the abnormal clones in this disease produce IgM macroglobulins. a milder disease than myeloma with longer survival rates and no bone pain, bone lesions, or renal disease.

Amyloidosis

deposits of abnormal proteins between cells of various organs, with the kidney and the heart most commonly affected.

Benign monoclonal gammopathy or Monoclonal gammopathy of undetermined significance (MGUS

an abnormal clonal disorder of the plasma cells, it secretes a myeloma-like protein into the blood but it rarely has clinical manifestations

Aspartate aminotransferase (AST)

an enzyme mainly found in the liver, heart, skeletal muscle, and kidneys which catalyzes the removal of an amino group from L-aspartate. used to diagnose liver disease, especially acute hepatitis

Alanine aminotransferase (ALT)

an enzyme predominantly found in the cytoplasm of liver cells, and with lesser activity in skeletal muscle, the kidney, heart, pancreas, lungs, spleen, and red blood cells. used to diagnose liver disease, especially acute hepatitis. elevations may also be seen in skeletal muscle diseases like myositis and muscular dystrophy

Gamma glutamyltransferase (GGT)

an enzyme predominantly found in the liver, kidneys, pancreas, and intestines. used primarily to diagnose hepatobiliary and hepatic disorders, also a sensitive indicator of alcohol abuse

5' Nucleotidase (NTP)

an enzyme found in cell membranes and distributed widely throughout the tissues of the body, levations reflect obstructive hepatobiliary disorders (but not bone disorders), making this enzyme useful in distinguishing between obstructive liver and bone diseases.

Alkaline Phosphatase (ALP)

found in high concentrations in liver and bone (most significant) and to a lesser extent in the intestines, kidney, and placenta. elevations may be seen in bone disease such as osteitis deformans (Paget's disease), pancreatitis, chronic renal failure, sepsis, thyrotoxicosis and with certain drugs, hepatic disease, especially hepatitis, jaundice and cirrhosis

Amylase (AMS)

found in many tissues but the most important are the pancreas and salivary glands. In acute pancreatitis levels rise within the first 8 hrs of an attack, peak at 12 - 48 hrs, and return to normal in 3 - 5 days. Macroamylase seen with increases levels. Decreases have been described in liver cirrhosis, liver malignancy, liver abscesses, and other hepatic diseases

Lipase (LPS)

almost exclusively produced in the pancreas. Elevations are indicative of diseases of the pancreas, parallels increases in amylase; however, may occur sooner and persist longer

Cholinesterases

Acetylcholinesterase (AChe) and Pseudocholinesterase (PChe). AChe is found in RBCs, the brain, and nerve cells.  PChe is found the serum, liver, pancreas, heart, and the white matter of nervous system. There may be decreased activity in liver disease following organophosphate (insecticide) poisoning

Glucose-6-phosphate dehydrogenase (G6PD)

found in the RBCs, adrenal glands, spleen, thymus, and lymph nodes. Decreased values may indicate a deficiency of G6PD which is an inherited sex-linked trait that precipitates a hemolytic event in the presence of oxidative stress (example: favism

Acid Phosphatase (ACP)

found in the liver, and kidneys but is in higher amounts in the prostate and in RBCs. Increased values may indicate prostatic or breast cancer with metastasis

Disorders of amino acid transport

These affect the movement of amino acids across cell membranes, often impacting renal reabsorption or intestinal absorption. Examples include cystinuria and Hartnup disease

Disorders of amino acid metabolism

These involve defects in enzymes responsible for breaking down specific amino acids. Examples include phenylketonuria (PKU) and maple syrup urine disease (MSUD)

Disorders of the urea cycle

These affect the body's ability to process and eliminate excess nitrogen, leading to ammonia accumulation. Examples include ornithine transcarbamylase deficiency and citrullinemia

Disorders of amino acid synthesis

These impair the body's ability to produce certain amino acids. An example is serine deficiency disorders