The cleavage of Hemoglobin and formation of pigments of bile, urine and feces

Hemoglobin is a main Protein of erythrocytes. Erythrocytes live 110-120 days. Then they are hemolyzed. Hemoglobin fallen out of erythrocytes and joins with haptoglobin. Such complex is transported to sites of cleavage of hemoglobin (liver and cells of macrophago-monocyte’s system).there haptoglobin is chipped off and hemoglobin beginns to destroy.

This process beginns from oxidative cleavage of methene bridge between first and second pyrrole rings of heme. It results in formation of verdoglobin. Then verdoglobin is broken up to biliverdin, iron and globin. Globin is destroyed as simple proteins to aminoacids and amino acids are broken up by deamination or decarboxylation. Iron exits in blood and binds with beta-globulins forming transferrin. Transferrin transfers iron in liver where it is stored as ferritin. Some of transferrin goe to marrow and there iron is used for biosynthesis of heme. But main substance of cleavage of verdoglobin is biliverdin. This is compound of green color and it is reduced by NADPH2 to undirect bilirubin. Bilirubin is a compound of brown-red color. It is also named non-conjugated (or free), insoluble and toxic.

This bilirubin is undirect because it doesn’t give direct color reaction with reagent Ehrlih. It gives this reaction only after addition of alcohol or coffeine reagent. Alcohol and coffeine reagent precipitate albumins and bilirubin may give color reaction with Ehrlih reagent. It isn’t bound to glucuronic acid therefore it is non-conjugated one. It is insoluble in water, hence it doesn’t transmit through kidneys and appears toxic action on brain.

Undirect bilirubin exits from macrophago-monocyte’s system into blood and there binds with albumins. Albumins prevent organism from its toxic action. Such complex achieves liver and albumins are chipped off. Undirect bilirubin undergoes conjugation with glucuronic acid and direct bilirubin is formed. Therefore it is also named conjugated (non-free one). This bilirubin is soluble in water due to glucuronic acids and may transmit through kidneys in urine, hence it is non-toxic.

Direct bilirubin and some of biliverdin are pigments of bile.

Direct bilirubin exits from liver and in choleductus it is converted to undirect bilirubin due to the chipping off glucuronic acids. Thus undirect bilirubin and some of biliverdin exit in small intestine. Undirect bilirubin is reduced into mesobilinogen (MBG), or urobilinogen (UBG) under influence of microbs of small intestine. A little mojety of MBG exits from small intestine into blood and enters the liver where it is broken up to mono- and dipyrroles (colorless substances) which exit in urine. A main mojety of MBG is converted to stercobilinogen (SBG) in large intestine. Some of SBG goes to kidneys where it is oxidized to stercobilin (pigment of urine). But bulky of SBG is oxidized in large intestine and it is pigment of feces. Some of biliverdin is pigment of feces too.

The color of blood serum depends on the presence of bilirubin. Total bilirubin of bloodserum is equal 8-20mcM/L and comprises from undirect (75%) and direct bilirubin (25%).