haptoglobin; contains: haptoglobin alpha chain; haptoglobin beta chain (HP)
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Function
- irreversibly binds alpha chain of free oxyhemoglobin
- prevents loss of iron through the kidneys & protects the kidneys from damage by hemoglobin, while making the hemoglobin accessible to degradative enzymes
- tetramer of two alpha & two beta chains formed from common precursor
- may form multimers of MW up to 1000 kD.
- normally accounts for 25% of the alpha-2 band on serum protein electrophoresis (SPE)
- an elevated haptoglobin is the most common abnormality seen on SPE
- haptoglobin is an acute phase reactant & becomes elevated non-specifically in the presence of inflammation or tissue injury
- depressed haptoglobin levels are seen in association with hemolysis
Structure
- belongs to the peptidase S1 family
- contains 1 peptidase S1 domain
- contains 2 Sushi (CCP/SCR) domains
Compartment
Expression
Polymorphism
- in human populations there are two major allelic forms, alpha-1 with 83 residues & alpha-2 with 142 residues
- these alleles determine the 3 major phenotypes HP*1F/HP*1S & HP*2FS
- the two main alleles of HP*1 are called HP*1F (fast) & HP*1S (slow)
Notes
- although homologous to serine proteases, it has lost all essential catalytic residues & has no enzymatic activity
More general terms
Additional terms
References
- ↑ Tietz Fundamentals of Clinical Chemistry 3rd ed, WB Saunders, 1987 pg 331
- ↑ Clinical Diagnosis & Management by Laboratory Methods, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1991, pg 222
- ↑ UniProt http://www.uniprot.org/uniprot/P00738.html
- ↑ GeneReviews http://www.ncbi.nlm.nih.gov/sites/genetests/lab/gene/HP
- ↑ SHMPD; Singapore Human Mutation and Polymorphism Database http://shmpd.bii.a-star.edu.sg/gene.php?genestart=A&genename=HP
- ↑ Wikipedia; Note: haptoglobin entry http://en.wikipedia.org/wiki/haptoglobin