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Histidine ball and stick model spinning. Histidine (symbol His or H) [2] is an essential amino acid that is used in the biosynthesis of proteins.It contains an α-amino group (which is in the protonated –NH 3 + form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO − form under biological conditions), and an imidazole side chain (which is partially ...
This histidine-rich glycoprotein contains two cystatin-like domains and is located in plasma and platelets.It is known that HRG binds heme, dyes, and divalent metal ions and it is thought to have multiple roles in the human blood, including roles in immunity, angiogenesis and coagulation. [15]
Mast cells are especially numerous at sites of potential injury – the nose, mouth, and feet, internal body surfaces, and blood vessels. Non-mast cell histamine is found in several tissues, including the hypothalamus region of the brain, where it functions as a neurotransmitter.
Hemes are most commonly recognized as components of hemoglobin, the red pigment in blood, but are also found in a number of other biologically important hemoproteins such as myoglobin, cytochromes, catalases, heme peroxidase, and endothelial nitric oxide synthase. [8] [9] The word haem is derived from Greek αἷμα haima 'blood'.
Fetal hemoglobin, or foetal haemoglobin (also hemoglobin F, HbF, or α 2 γ 2) is the main oxygen carrier protein in the human fetus.Hemoglobin F is found in fetal red blood cells, and is involved in transporting oxygen from the mother's bloodstream to organs and tissues in the fetus.
Hemoglobin S (α 2 β S 2) – A variant form of hemoglobin found in people with sickle cell disease. There is a variation in the β-chain gene, causing a change in the properties of hemoglobin, which results in sickling of red blood cells. Hemoglobin C (α 2 β C 2) – Another variant due to a variation in the β-chain gene.
The enzyme histidine decarboxylase (EC 4.1.1.22, HDC) is transcribed on chromosome 15, region q21.1-21.2, and catalyzes the decarboxylation of histidine to form histamine. In mammals, histamine is an important biogenic amine with regulatory roles in neurotransmission , gastric acid secretion and immune response .
Carnosine is a dipeptide composed of beta-alanine and histidine, and is found in skeletal muscle and cells of the nervous system. [6] This disorder results in an excess of carnosine in the urine, cerebrospinal fluid, blood, and nervous tissue. [7]