PROTEINSAlbumin

&Globulin

رجاء : الكيمياوية اعدادعبود

Contents: Total proteinAlbumin GlobulinA/G (ALBUMIN/GLOBULIN) ratio

Proteinurea Microalbuminuria/(ACR)Porotein in other body fluids

Total proteins

DefinitionProteinA large class of complex organic chemical compounds that are essential for life. Proteins play a central role in biological processes and form the basis of living tissues .

They consist of long chains of amino acids connected by peptide bonds .

Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs; and each protein has unique functions. Examples are

hormones enzymesand antibodies.

Unlike carbohydrates and fats, proteins are not stored in the body.

They are continuously broken down (metabolized) into amino acids that can be used to make new proteins, hormones, enzymes, and other compounds needed by the body .

Amino acidsAre biologically important organic compounds made from amine  group

-(NH2 )and carboxylic acid  group

-(COOH, ) functional groups , along with a -side chain  s pecific to each aminoacid.The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids.

Zwitter ion amino acids contains a negative

carboxylate and a positive ammonium group,so has net zero charge. This molecular state is known as a zwitter ion,it is a neutral molecule.

A peptide bond (amide bond) Is a covalent chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, causing the release of a molecule of water (H2O), and usually occurs between amino acids.

ProteinsFrom the Greek proteios, meaning first are a class of organic compounds which are present in and vital to every living cell,they are macromolecules made up of amino acid linked together by peptide bonds  .

In the form of skin, hair, cartilage, muscles, tendons and ligaments.

proteins hold together, protect, and provide structure to the body of a multi-celled organism

Proteins In the form of enzymes, hormones, antibodies, and globulins, they catalyze, regulate, and protect the body chemistry.

In the form of hemoglobin, myoglobin and various lipoproteins, they effect the transport of oxygen and other substances within an organism.

classification of protein’s amino acidsProteins are made up of some 20

different amino acids,they are classified into :

1-Essential amino acids

They are nine A.As,they cannot be synthesised in humans but are required for synthesis of important proteins . they are supplied by meat and dairy products

2-Nonessential amino acids They are produced by our bodies, even if

we don't get it from the food we eat.

3-Conditional amino acidsThey can be synthesised from other

amino acids, provided there is an adequate dietary supply .

The ‘biological’ value of different proteins depends on the relative proportions of essential amino acids they contain.

Proteins of animal origin, particularly from eggs, milk and meat, are generally of higher biological value than proteins of vegetable origin, which are low in one or more of the essential amino acids .

Essential Amino Acids

Non-Essential Amino Acids

histidineisoleucineleucinelysinemethioninephenylalaninethreoninetryptophanvaline

alaninearginine*aspartic acidcysteine*glutamic acidglutamine*glycine*proline*serine* tyrosine*asparagine*selenocysteine*conditionally essential

Types of Amino AcidAliphatic Amino Acids .Aromatic Amino Acids .Sulphur containing Amino Acids .Acidic Amino Acids .Basic Amino Acids .Neutral Polar Amino Acids .

Families of blood proteins Serum albumin accounts for 55% of blood proteins, and is a major contributor to maintaining the osmotic pressure of plasma to assist in the transport of lipids and steroid hormones.

Globulins make up 35% of blood proteins and transport ions, hormones and lipids assisting in immune function. 

Fibrinogen  make up 7% of blood proteins; conversion of fibrinogen to insoluble fibrin is essential for blood clotting.

The remainder of plasma proteins (3%) is made up of regulatory proteins such as enzymes, proenzymes and hormones.

All blood proteins are synthesized in liver except for the gamma globulins .

Families of blood proteins

Protein SynthesisProteins are synthesized in the body through a process called translation. Translation occurs in the cytoplasm and involves the translation of genetic codes, unit during DNA transcription, into proteins. Cell structures called ribosomes help translate these genetic codes into polypeptide chains that undergo several modifications before becoming fully functioning proteins.

The hepatocyte (liver ) is the site  that manufactures serum albumin, fibrinogen, and the prothrombin group of clotting factors .

It is the main site for the synthesis of lipoproteins, ceruloplasmin, transferrin,

 complement, and glycoproteins. Hepatocytes also manufacture their

intracellular enzymes .  immunoglobulins are  produced

by liver and immune system .

The digestion of proteinThe digestion of protein begins in the mouth with chewing.

Protein digestion continues in the stomach with the release of hydrochloric acid and pepsinogen. Hydrochloric acid converts pepsinogen into pepsin, which begins to break down the bonds between the amino acids.

Your body uses the individual amino acids that were broken down during digestion to build the proteins needed for the various functions .

 Glucogenic amino acids can also be converted into glucose, through gluconeogenesis.

FUNCTIONS OF PROTEINSMovementWithout proteins, you could not move, bend or even stand up straight.

Proteins support your connective tissues, which are found in your tendons, ligaments and bones. These tissues connect your joints and allow movement.

Other proteins, called actin and myosin, permit your muscles to contract. This allows you to run, sit and lie down.

Immune ResponseAntibodies - are specialized proteins

involved in defending the body from antigens (foreign invaders).

They can travel through the blood stream and are utilized by the immune system to identify and defend against bacteria, viruses, and other foreign intruders.

Transport Proteins are carrier proteins which move

molecules from one place to another around the body. Examples include hemoglobin and cytochromes.

Hemoglobin transports oxygen through the blood.

Cytochromes operate in the electron transport chain as electron carrier proteins.

Acid-Base BalanceProteins also serve as buffers, helping

maintain the pH of a solution. When your blood becomes too acidic,

protein side chains pick up excess hydrogen ions to increase the pH of your blood.

If your blood becomes too basic, or alkaline, other protein side chains donate hydrogen ions to decrease the pH.

Fluid BalanceYour body contains approximately 60 percent water, making it the most abundant substance in your body. For you to stay healthy, this water must disperse properly throughout your body, and proteins help do this.

Proteins attract water, so they can pull fluid into capillaries and prevent it from accumulating in your body tissues. Without proteins, your body tissues would become bloated, leading to generalized swelling called edema.

Enzymes are proteins that facilitate biochemical reactions.

They are often referred to as catalysts because they speed up chemical reactions. Examples include the enzymes lactase and pepsin.

Lactase breaks down the sugar lactose found in milk.

Pepsin is a digestive enzyme that works in the stomach to break down proteins in food.

Hormonal ProteinsAre messenger proteins which help to

coordinate certain bodily activities. Examples include :

insulin, oxytocin, and somatotropin. Insulin regulates glucose metabolism

by controlling the blood-sugar concentration.

Oxytocin stimulates contractions in females during childbirth.

Somatotropin is a growth hormone that stimulates protein production in muscle cells. 

Priciple of determinationBIURET methodBIURET reagent :Sodium hydroxide, Na-K Tartrate, Potassium Iodide, Copper sulfate

The peptide bonds of protein react with Cu⁺⁺ in alkaline solution to form a colored complex which absorbance, proportional to the concentration of total protein in the specimen .

NORMAL VALUES: (64 -83) g/l .

serum albumin

Definition :serum albumin,is aprotein found in blood plasma that helps maintain the osmotic pressure between the blood vessels and tissues and serves as a carrier for many substances .

Serum albumin accounts for abuot 55 percent of the total protein in blood plasma .

It is important for tissue growth and healing.Very stable protein with a high net negative charge at physiological PH .

Water-soluble .Moderately soluble in concentrated salt solutions 

Experience heat denaturation . It stay in the blood for about 20 days .

SynthesisAlbumin is synthesized in the liver aspreproalbuminProalbuminAlbuminAlbumin is not stored by the liver but is secreted into the portal circulation as soon as it is manufactured.

Damaged liver cells lose their ability to make albumin . 

But previously produced albumin may stay in the blood for a bout 18 days, so it takes about 2 weeks for damage to the liver to show up as decreased serum albumin levels. 

The liver's ability to make albumin may be used to predict the course of certain liver diseases.

Function of albumin1- Albumin is responsible for much of the colloidal osmotic pressure of the blood, and thus is a very important factor in regulating the exchange of water between the plasma and the interstitial compartment (space between the cells) .

Because of hydrostatic pressure, water is forced through the walls of the capillaries into the tissue spaces. 

This flow of water continues until the osmotic pull of protein (albumin) molecules causes it to stop. 

A drop in the amount of albumin in the plasma leads to an increase in the flow of water from the capillaries into the interstitial compartment. 

This results in an increase in tissue fluid which, if severe, becomes apparent as edema. 

2-  Albumin serves also as a transport protein The presence of many charged surface groups plus many binding sites, both ionic and hydrophopic,gives albumin the ability to bind and transport a large number of compounds such as  :

fatty acidsbilirubinmany drugs

And also hormones, such as cortisol and thyroxine, when their specific binding globulins are saturated.

Albumin also acts as a carrier for two materials necessary for the control of blood clotting:

(1) antithrombin, which keeps the clotting enzyme thrombin from working unless needed, and

(2) heparin cofactor, which is necessary for the anticlotting action of heparin.

3- Acid–base function, it can act as an effective plasma buffer.

4- Antioxidant function .Under physiological conditions, albumin may have significant antioxidant potential. It is involved in the getting rid off of oxygen free radicals, which have been involved in the pathogenesis of inflammatory diseases .

Clinical significance  (Hyperalbuminemia) : High albumin concentrations in plasma .

There are no pathological conditions other than dehydration associated with a high albumin concentration. 

With prolonged use of a tourniquet .After excessive albumin infusion . Some drugs like , steroids, androgens, growth hormones, and insulin.

(Hypoalbuminemia ) low blood albumin levels can be caused by:

1- Nephrotic syndrome .It occurs when the filters in the kidney leak an excessive amount of protein. 

The level of protein in the blood then falls and this allows fluid to leak across very small blood vessels into the tissues. 

Swelling around the eyes, abdomen and legs is then noted. 

2 - Liver failure is the inability of the liver to perform its normal synthetic and metabolic function as part of normal physiology. 

Two forms are recognised, acute and chronic.

Acute liver failure is defined as "the rapid development of hepatocellular dysfunction, specifically coagulopathy and mental status changes (encephalopathy), (disease in which the functioning of the brain is affected by some agent or condition (such as viral infection or toxins in the blood).

Chronic liver failure ,usually occurs in the case of cirrhosis, itself potentially the result of many possible causes, such as: excessive alcohol intake Hepatitis B or C, Autoimmune, hereditary and metabolic causes (such as iron or copper overload ) .

3- MalabsorptionIt is a state arising from abnormality in absorption of food nutrients across the gastrointestinal (GI) tract.

Impairment can be of single or multiple nutrients depending on the abnormality. 

This may lead to malnutrition and a variety of anaemias.

4 - protein losing enteropathyProtein losing enteropathy (pathological conditions in the intestines that are characterized by the gastrointestinal loss of serum proteins, including serum albumin; immunoglobulins) .

Common causes of protein losing enteropathy include celiac disease, Crohn's disease, short bowel syndrome (where the absorptive area for proteins is decreased). 

5 -Water overloadwater intoxication, also known as water poisoning, If a large amount of fluid is consumed over a short period of time, the cells will begin to swell because the kidneys cannot process the water quickly enough. The water starts to dilute the electrolyte levels in the body, and if enough water is consumed, the cells could actually burst. A low level of electrolytes can result in an irregular heartbeat, brain malfunction, and ultimately death.

 6 - Intestinal enteropeptidase deficiency

Enteropeptidase is an enzyme  secreted from intestinal glands following the entry of ingested food passing from the stomach.  Enteropeptidase converts trypsinogen  into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes.

7- BurnsThere is massive protein loss from the burn site due to :

 increased vascular permeability .decreased albumin synthesis .and protein losing nephropathy. 

 8- KwashiorkorIt is an acute form of childhood protein-energy malnutrition  .

It may develop after a mother stop feeding her child from breast milk, replacing it with a diet high in carbohydrates, especially starches, but deficient in protein.

occurs in areas of famine or poor food supply.  Cases in the developed world are rare.

 9- Other causes Fluid retention, as in pregrant women during late pegrancy .

Administration of an excess of protein –free fluid .

Recumbency,plasma albumin con. May be 5-10% g/l lower in the recumbent than in the upright position because of the redistribution of fluid .

Artefactual changes ,due to taking blood from the arm into which an infusion is flowing .

Priciple of determinationBROMOCRESOL GREEN methodBROMOCRESOL GREEN reagentSuccinic acid, Bromocresol green, Sodium hydroxide .

In buffer solution at PH 4.2,Bromocresol green + albumin        colored compound .

NORMAL VALUES: (34 − 48) g/L .

  certain drugs increase albumin in the blood, including anabolic steroids, androgens, growth hormones, and insulin .

 Transfusions of serum albumin are used to combat shock and whenever it is necessary to remove excess fluid from the tissues.

GLOBULINS

Definition Any of a class of proteins that are found extensively in blood plasma, milk, muscle, and plant seeds and that are insoluble in pure water, soluble in dilute salt solution, and coagulable by heat.

They play a key role in the body's immune system and act as a carrier .

The plasma globulins are separated into four major groups by serum protein electrophoresis (SPE) according to size and charge these fractions are :

Alpha1

Alpha2

BetaAnd the gamma globulins,which usually makes up the largest portion of the globulins .

SynthesisSome globulins are produced in the liver, while others are secreted by the immune system.

most of the proteins in the alpha and beta fractions are made in the liver.

γ globulins are produced by lymphocytes and plasma cells in lymphoid tissue.

FunctionThe globulins include carrier proteins, which transport specific substances(transferrin that transports iron).

acute phase reactants, which are involved in the inflammatory process (C-reactive protein) .

clotting factors ( fibrinogen ). complement components.And immunoglobulins,(IgM, IgA, IgG, IgE ).

Clinical significanceThe globulin level may be elevated in:

Chronic infections (parasites, some cases of viral and bacterial infection) .

Liver disease (biliary cirrhosis, obstructive jaundice).

Carcinoid syndrome.Rheumatoid arthritis.Ulcerative colitis.Multiple myelomas, leukemias .

Autoimmunity (Systemic lupus, collagen diseases ) .

Kidney dysfunction (Nephrosis) .

The serum globulin level may be decreased in:

Nephrosis .Alpha-1 Antitrypsin Deficiency (Emphysema),it is a long-term lung disease.

Acute hemolytic anemia .Liver dysfunction .Hypogammaglobulinemia/Agammaglobulinemia .

For the routine chemistry profile, total globulins are calculated as follows:

TP - albumin = globulin

NORMAL VALUES: (27 − 39) g/L .

A/G (ALBUMIN/GLOBULIN) RATIO

The ratio of albumin to globulin can also help determine whether certain disorders are occurring.

The A/G ratio may provide a clue as to the cause of the change in protein levels.

The proper albumin to globulin ratio is 2:1 Optimal Range: 1.7-2.2

The AG ratio may be elevated in:Hypothyroidism .High protein/high carbohydrate diet with poor nitrogen retention .

Hypogammaglobulinemia (low globulin) .

Glucocorticoid excess .

The AG ratio may be decreased in:Liver dysfunction .Overproduction of globulin .an underproduction of albumin loss of albumin due to kidney disorders .

Proteinurea

Definition Proteinuria(from protein and urine) means the presence of an excess of serum proteins in the urine. 

The condition is often a sign of kidney disease.

Healthy kidneys do not allow a significant amount of protein to pass through their filters. But filters damaged by kidney disease may let proteins such as albumin leak from the blood into the urine.

The mechanism

Albumin (when ionized in water at pH 7.4, as found in the body) is negatively charged.

The glomerular basement membrane is also negatively charged in the body; some studies suggest that this prevents the filtration of albumin in the urine.

According to this theory, that charge plays a major role in the selective exclusion of albumin from the glomerular filtrate.

Causes includeDue to disease in glomerulus .Because of increased quantity of proteins in serum (overflow proteinuria).

Due to low reabsorption at proximal tubule (Fanconi syndrome) .

Diabetes .High blood pressure (hypertension) .

Preeclampsia (high blood pressure and proteinuria in pregnancy) .

Excessive fluid intake (drinking in excess of 4 litres of water per day) .

Some medications used in cancer treatment.

With cardiovascular disease .Severe emotional stress .severe exercise .Age over  65 .

Measurement A semi-quanititative test such as a dipstick urine protein is used to screen for the presence of protein in the urine as part of a routine urinalysis.

If slight to moderate amounts of protein are detected, then a repeat urinalysis and dipstick protein may be performed at a later time to see if there is still protein in the urine or if it has dropped back to undetectable levels .

If there is a large amount of protein in the first sample and/or the protein persists in the second sample, then a 24-hour urine protein may be used as a follow-up test.

Since the dipstick primarily measures albumin, the 24-hour urine protein test then may be ordered to find if there is proteins other than albumin are being released.

A 24-hour urine sample gives the protein excretion rate over 24 hours. It will be accurate only if all of the urine is collected. 

The reagent on the test strips, bromphenol blue,which is highly specific for albumin.

False negative reading If the urine is dilute .if the protein in the urine is composed mainly ofglobulins or Bence-Jones proteins .

Dye (contrast media) if you have a radiology scan within 3 days before the urine test .

Severe emotional stress .Strenuous exercise .Urinary tract infection .

Urine contaminated with fluids from the vagina .

The normal value is less than 80 milligrams per day .

Protein dipstick grading

DesignationApprox. amount

Concentration[ Daily

Trace 5–20 mg/dL

1+ 30 mg/dL Less than 0.5 g/day

2+ 100 mg/dL 0.5–1 g/day

3+ 300 mg/dL 1–2 g/day

4+ More than 2000 mg/dL

More than 2 g/day

microalbuminuria

Definition It is a very small increase in urinary albumin below the detection level of routine dipstick analysis. The condition is an early indicator of altered glomerular permeability .

In a properly functioning body, albumin is not normally present in urine because it is retained in the bloodstream by the kidneys.

Microalbuminuria can be diagnosed from a 24-hour urine collection (between 30–300 mg/24 hours) or, more commonly, from elevated concentrations in a spot sample (30 to 300 mg/L).

Both must be measured on at least two of three measurements over a two- to three-month period.

Measurement of albumin excretion in a 24-h urine collection has long been the “gold standard” for quantitative evaluation of albuminuria ,however, collection errors due to improper timing and missed samples may lead to significant over- and underestimation of albuminuria.

For convenience and accuracy the American Diabetes Association and the National Kidney Foundation have recently recommended measurement of albumin-to-creatinine ratio (ACR) .

For convenience and consistency, the American Diabetes Association and the National Kidney Foundation have recently recommended measurement of albumin-to-creatinine ratio (ACR) in a random spot urine collection for diagnosis of microalbuminuria. 

For the diagnosis of microalbuminuria, care must be taken when collecting sample for the urine ACR. 

An early morning sample is preferred.

 The patient should stop doing heavy exercises 24 hours before the test.

A repeat test should be done 3 to 6 months after the first positive test for microalbuminuria.

The test is inaccurate in :A person with too much or too little muscle mass. This is due to the variation in creatinine level which is produced by the muscle.

Women during the menstrual cycle .If there is more than 7 pus cell .If there is more than 3 RBC .

Clinical SignificanceAn indicator of subclinical cardiovascular disease

An important prognostic marker for kidney disease .In diabetes mellitus .In hypertension .In Post-streptococcal glomerulonephritis .

Normal valueMen- < 2.5 (mg/mmol) or < 23 (mg/g)Women - < 3.5 (mg/mmol) or < 32 (mg/g)

Porotein in other body fluids

Ascites fluid : it is an accumulation of fluid in the peritoneal cavity .

The most common due to cirrhosis, severe liver disease or metastatic cancer .

 Patients with ascites generally will complain of progressive abdominal heaviness and pressure as well as shortness of breath .

 Pleural fluid : It is excess fluid that accumulates between the two pleural layers, the fluid-filled space that surrounds the lungs .

Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during ventilation.

CSF total protein : (CSF) is the fluid that surrounds the brain and spinal cord.

This test is done to determine the amount of protein in the spinal fluid, also called cerebrospinal fluid (CSF).

To help diagnose tumors, infection, inflammation of several groups of nerve cells, vasculitis, blood in the spinal fluid, or injury.

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