Biochemistry I: Plasma Proteins PDF

19 Mays Abu Sara Heba Dajah Nabil Bashir Plasma Proteins Biochemistry I Ist semester Overview: • Functions and characteristics of plasma proteins • Measurement of plasma proteins and diagnosis of diseases • Electrophoretic patterns of plasma proteins • Acute phase proteins Modified:  Before...

19 Mays Abu Sara Heba Dajah Nabil Bashir Plasma Proteins Biochemistry I Ist semester Overview: • Functions and characteristics of plasma proteins • Measurement of plasma proteins and diagnosis of diseases • Electrophoretic patterns of plasma proteins • Acute phase proteins Modified:  Before you start, let’s revise some information (from ur previous knowledge :’) We know that if you take a blood sample and centrifuge it you will end with 3 bands : cells (hematocrit , Buffy coat) + plasma. • Plasma : the liquid component of the blood make 55% of it, contains 92% water + 8% solids (dissolved in the plasma). • One of these solids is the proteins which we called plasma protein, and that’s our topic in these slides. • We have 2 concepts: plasma & serum →serum = plasma – fibrinogen(protein important in coagulation) ‫مصل‬ Plasma Proteins  Plasma contains >300 different proteins  Many pathological conditions affect level of plasma proteins  Mostly synthesized in the liver  Some are produced in other sites  A normal adult contains ~70 g/L . Modified • Many pathological conditions affect level of plasma proteins: ➢ If there is a liver or kidney disease, infection, inflammation or any other pathological condition will affect the protein concentration in the plasma, for example if the typical concentration for albumin is 70g/L ,in liver disease you may have just 30g/L. • A normal adult contains ~70 g/L : ➢ 70 g/L = 7 g/dL ،‫(الدكتور حكى رح يجيب عليها سؤال على االغلب رح يسأل عن تركيزه الطبيعي بس يغير الوحدة‬ ‫انتبهوا للرقم في حال جابه ا‬ ) 🙂 ‫فعًل وبأكتر من ِوحدة مشان الدكاترة بحبو األرقام‬ Functions of plasma proteins • Transport (Albumin, prealbumin, globulins) →of many things: FA, hormones, metals… • Maintain plasma oncotic pressure (Albumin) →oncotic pressure that maintain balance of fluid in the body, Albumin make 80% of this function. • Defense (Immunoglobulins and complement) • Clotting and fibrinolysis (Thrombin and plasmin) ‫وظيفة خاصة بسبب وجود شكل محدد‬ General functions ➢ ➢ A nutritive role Maintenance of blood pH (amphoteric property) →they act as a buffer because they have weak acid&base groups. ➢ ➢ Contributes to blood viscosity(Albumin+fibrinogen mainly) Maintenance of blood osmotic pressure Specific functions Enzymes (e.g. rennin, coagulation factors, lipases) ➢ Humoral immunity (immunoglobulins) ➢ Blood coagulation factors ➢ Hormonal (Erythropoietin) ➢ Transport proteins (Transferrin, Thyroxin binding globulin, Apolipoprotein) ➢ Measurement of Plasma Proteins A) Quantitative measurement of a specific protein: Chemical (Biuret), A280 →By chemical reagents such as Biuret reagent, called colorimetric method: -we use biuret reagent that composed of alkaline copper sulfate, and it will react with the peptide bond and make a coloured compound that could be measured by light absorption, and light absorption proportional to concentration by a law called Beer-Lambert’s Law. -A280: another method on the same way. ّ ‫باختصار‬ ‫بنعرض املركب (البروتين) لضوء وبنشوف مقدارامتصاصه لطول موجي معين وهاد املقدار بكون متناسب مع‬ .‫تركيزه عن طريق قانون رياض ي (مش مطلوب نعرفه) وهيك بنكون عرفنا التركيز‬ -we don’t have to know more details, focus on the next method. B) Semiquantitative measurement by electrophoresis:  Proteins are separated by their electrical charge in electrophoresis  Five separate bands of proteins are observed  These bands change in disease -First, we put the sample of plasma then connect the device with electrical power, and by electrical current the protein in the sample will migrate in different regions according to their charges mainly. -After electrophoresis we take the sample and stain it, the proteins that migrate into different regions will bind to the stain according to their concentration which means that thickness of the band proportional to concentration, so we have different bands and each band represent certain proteins that separated by their charges. →Increase in thickness, increase in concentration ً ‫هاي الطريقة بتفصل‬‫اعتمادا على الحجم كمان فبنستدل انه اقرب باند للموجب‬ ً ‫هي اصغر وحدة‬ .‫حجما بس الدكتور ركز على انه يتم فصلهم حسب الشحنة‬ Normal Pattern of Plasma Protein Electrophoresis Notes: →Hight of the peak proportional to concentration. →Hight of the peak will be different under pathological conditions, For ex: if the peak of albumin depressed so we know that we have hypoalbuminemia(low concentration) -It assume that here we must have fibrinogen peak, but concentration is very low so it doesn’t appears. A -Every peak contain many types of proteins (so the band does not have one protein only), except the band and peak of albumin express only albumin, same thing for the fibrinogen but doesn’t appear. -Albumin & Prealbumin have high –ve charge because of their structure (their amino acid have -ve R groups such as glutamate & aspartate) , so the more the negativity more migration away from –ve in electrophoresis. Types of Plasma Proteins  Prealbumin →(have a beak before the albumin if it appears, that’s the cause of the name)  Albumin  α1-Globulins:  1-Antitrypsin, α-fetoprotein  α2-Globulins:  Ceruloplasmin, haptoglobin  β-Globulins:  CRP, transferrin, β2-microglobulin  γ- Globulins Prealbumin (Transthyretin)  Pre-albumin is not the precursor of albumin, it has its name because its beak before albumin beak, it’s completely different from albumin and it’s have the highest negative charge.  A transport protein for:  Thyroid hormones  Retinol (vitamin A)  Migrates faster than albumin in electrophoresis  Lower levels found in: Kidney disease (there is secretion but no absorption)  liver disease, nephrotic syndrome, acute phase inflammatory responses (here the body needs to secrete more acute phase proteins and pre-albumin doesn’t consider acute protein so the liver decrease its synthesis), malnutrition ً )‫رح تتوضح النقطة الحقا ؛‬  Short half-life (2 days) ّ ‫الوقت الي رح ياخذه البروتين لحتى تقل‬ Half-life : ‫كميته للنصف‬ Albumin  Most abundant plasma protein (~40 g/L) in normal adult  Synthesized in the liver as preproalbumin and secreted as albumin →preproalbumin is the precursor of albumin and the largest in size, its not functional so it cleaved twice to be secreted as albumin Prepro → pro → albumin  Half-life in plasma: 20 days  Decreases rapidly in injury, infection and surgery Functions • Maintains oncotic pressure: – The osmotic pressure exerted by plasma proteins that pulls water into the circulatory system – Maintains fluid distribution in and outside cells and plasma volume • 80% of plasma oncotic pressure is maintained by albumin ➢ Albumin decreases → oncotic pressure decreases → fluid accumulate outside cells → causing edema ‫آلبيومن جوا األوعية الدموية فبحافظ على مستوى الماء الي برا الوعاء أي‬-‫ عادة ً بيتركز ال‬: ‫توضيح بسيط للفهم‬ ‫تغيير فيه رح ترجعه للرينج الطبيعي لكن في حالة قلت كمية البروتين ألسباب معينة ف رح يبطل في محافظة‬ Edema ‫والسوائل الي داخل األوعية رح تصيرتطلع لبرا مسببة ال‬ Functions • A non-specific carrier of – hormones, calcium, free fatty acids, drugs, etc. • Nutritional function, Tissue cells can take up albumin by pinocytosis where it is hydrolyzed to amino acids • Useful in treatment of liver diseases, hemorrhage, shock and burns (because it maintains fluid,blood pressure) Hypoalbuminemia (decreased in albumin) Hypo : low Albuminemia : concentration of albumin in plasma • Causes – Decreased albumin synthesis (liver cirrhosis, malnutrition(shortness of amino acid that important in synthesizing albumin) ) – Increased losses of albumin • Increased catabolism in infections • Excessive excretion by the kidneys (nephrotic syndrome) • Excessive loss in bowel • Severe burns (plasma loss in the absence of skin barrier) Hypoalbuminemia Effects • Edema due to low oncotic pressure – Albumin level drops in liver disease causing low oncotic pressure – Fluid moves into the interstitial spaces causing edema • Reduced transport of drugs and other substances in plasma • Reduced protein-bound calcium – Total plasma calcium level drops – Ionized calcium level may remain normal Hyperalbuminemia (increased in albumin, rare case) • No clinical conditions are known that cause the liver to produce large amounts of albumin • The only cause of hyperalbuminemia is dehydration