Haptocorrin
Encyclopedia
Haptocorrin also known as transcobalamin-1 (TC-1) is a protein
that in humans is encoded by the TCN1 gene
. The essential function of haptocorrin is protection of the acid-sensitive vitamin B12
while it moves through the stomach.
produced by the salivary glands of the oral cavity, in response to ingestion of food. This protein binds strongly to vitamin B12
(Vit. B12), or as it is sometimes referred to, cyanocobalamin
, in what is perhaps an intricate yet necessary evolutionary mechanism to protect this vitamin from the acidic environment of the stomach. Vitamin B12 is an essential water soluble vitamin, the deficiency of which creates anemia (macrocytic anemia), decreased bone marrow cell production (anemia
, pancytopenia
), neurological problems (tabes dorsalis
), as well as metabolic issues (methylmalonyl-CoA acidosis
).
Vitamin B12 is therefore an important vitamin for the body to absorb; despite its vital role however, vitamin B12 is structurally very sensitive to the hydrochloric acid
found in the stomach secretions, and easily denatures in that environment before it has a chance to be absorbed by the small intestine; found in fresh animal products (such as liver), vitamin B12 attaches haptocorrin, which has a high affinity for its molecular structure. Coupled together vitamin B12 and haptocorrin create a complex. This "Haptocorrin-Vit. B12" complex is impervious to the insult of the stomach acid, and passes on via the pylorus to the duodenum. In the duodenum pancreatic proteases (a component of pancreatic juice
) cleave haptocorrin, yet again releasing vitamin B12 in its free form.
The same cells in the stomach that produce gastric hydrochloric acid, the parietal cells, also produce a molecule called the intrinsic factor
(IF), which rebinds the B12 after its release from haptocorrin by digestion, and without which vitamin B12 can not be absored. Intrinsic factor (IF) is a glycoprotein, with a MW of 45,000 dalton. In the duodenum, the free vitamin B12 attaches the intrinsic factor (IF) to create a "vitamin B12-IF" complex. This complex then travels through the small bowel and reaches the terminal tertiary portion of the small intestine, called ileum
. Ileum is the shortest of all portions of the small intestine, but has on its surface specialized receptors called "cubilin
" receptors, that identify the "Vit. B12-IF" complexs and take them up into the circulation via endocytosis
mediated absorption.
In short, the essential function of haptocorrin is protection of the acid-sensitive vitamin B12 while it moves through the stomach.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that in humans is encoded by the TCN1 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
. The essential function of haptocorrin is protection of the acid-sensitive vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
while it moves through the stomach.
Function
Haptocorrin (HC), also commonly known as the R-protein, or the R-factor, or previously referred to as "transcobalamin I", is a unique glycoproteinGlycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
produced by the salivary glands of the oral cavity, in response to ingestion of food. This protein binds strongly to vitamin B12
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...
(Vit. B12), or as it is sometimes referred to, cyanocobalamin
Cyanocobalamin
Cyanocobalamin is an especially common vitamer of the vitamin B12 family. It is the most famous vitamer of the family, because it is, in chemical terms, the most air-stable...
, in what is perhaps an intricate yet necessary evolutionary mechanism to protect this vitamin from the acidic environment of the stomach. Vitamin B12 is an essential water soluble vitamin, the deficiency of which creates anemia (macrocytic anemia), decreased bone marrow cell production (anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, pancytopenia
Pancytopenia
Pancytopenia is a medical condition in which there is a reduction in the number of red and white blood cells, as well as platelets.If only two parameters from the full blood count are low, the term bicytopenia can be used...
), neurological problems (tabes dorsalis
Tabes dorsalis
Tabes dorsalis is a slow degeneration of the sensory neurons that carry afferent information. The degenerating nerves are in the dorsal columns of the spinal cord and carry information that help maintain a person's sense of position , vibration, and discriminative touch.-Cause:Tabes dorsalis is...
), as well as metabolic issues (methylmalonyl-CoA acidosis
Methylmalonic acidemia
Methylmalonic acidemia , also called methylmalonic aciduria, is an autosomal recessive metabolic disorder. It is a classical type of organic acidemia....
).
Vitamin B12 is therefore an important vitamin for the body to absorb; despite its vital role however, vitamin B12 is structurally very sensitive to the hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
found in the stomach secretions, and easily denatures in that environment before it has a chance to be absorbed by the small intestine; found in fresh animal products (such as liver), vitamin B12 attaches haptocorrin, which has a high affinity for its molecular structure. Coupled together vitamin B12 and haptocorrin create a complex. This "Haptocorrin-Vit. B12" complex is impervious to the insult of the stomach acid, and passes on via the pylorus to the duodenum. In the duodenum pancreatic proteases (a component of pancreatic juice
Pancreatic juice
Pancreatic juice is a liquid secreted by the pancreas, which contains a variety of enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, and amylase....
) cleave haptocorrin, yet again releasing vitamin B12 in its free form.
The same cells in the stomach that produce gastric hydrochloric acid, the parietal cells, also produce a molecule called the intrinsic factor
Intrinsic factor
Intrinsic factor also known as gastric intrinsic factor is a glycoprotein produced by the parietal cells of the stomach. It is necessary for the absorption of vitamin B12 later on in the small intestine...
(IF), which rebinds the B12 after its release from haptocorrin by digestion, and without which vitamin B12 can not be absored. Intrinsic factor (IF) is a glycoprotein, with a MW of 45,000 dalton. In the duodenum, the free vitamin B12 attaches the intrinsic factor (IF) to create a "vitamin B12-IF" complex. This complex then travels through the small bowel and reaches the terminal tertiary portion of the small intestine, called ileum
Ileum
The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...
. Ileum is the shortest of all portions of the small intestine, but has on its surface specialized receptors called "cubilin
Cubilin
Cubilin is a protein that in humans is encoded by the CUBN gene.- Function :Cubilin acts as a receptor for intrinsic factor-vitamin B12 complexes. The role of receptor is supported by the presence of 27 CUB domains. Cubulin is located within the epithelium of intestine and kidney. Mutations in...
" receptors, that identify the "Vit. B12-IF" complexs and take them up into the circulation via endocytosis
Endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
mediated absorption.
In short, the essential function of haptocorrin is protection of the acid-sensitive vitamin B12 while it moves through the stomach.