Wednesday, 6 May 2015

Hemoglobin

1) Hemoglobin D-Punjab – (α2βD2) 

results from a GAA ->CAA mutation at codon 121 glutamic acid changed to glutamine
most common form is called Hb D-Punjab after the area in India and Pakistan where it is most frequent 
a/k/ as ---- Hb D-Los Angeles 
Hemoglobin D co-migrates with hemoglobin S at alkaline pH
Hb D does not sickle

2) Hemoglobin H (β4) – 
due to 3 alpha gene deletion. 
formed by a tetramer of β chains 
variants of α-thalassemia.
3) Hemoglobin Barts (γ4) –
Due to deletion of all 4 alpha genes
formed by a tetramer of γ chains
variants of α-thalassemia.

4) Hemoglobin S (α2βS2) – 
caused by a point mutation in the β-globin chain of haemoglobin, 
glutamic acid is replaced by valine at the sixth position of β-globin gene (on chromosome 11)
5) Hemoglobin M:-
group of abnormal Hb's in which a single amino acid substitution favors the formation of methemoglobin in spite of normal quantities of methemoglobin reductase.
Strictly speaking, Hb M are Hb's with mutations at the proximal or distal histidyl residues. Other Hb's M tend to favor the Fe(III) state. 
Heterozygotes have congenital methemoglobinemia; the homozygous state of these genes is unknown and is presumably lethal. 
Specific types include: 
Hb MIwate, α87His→Tyr (α chain, position 87, histidine replaced by tyrosine);
Hb M Hyde Park, β92His→Tyr; 
Hb MBoston, α58His→Tyr; 
Hb MSaskatoon, β63His→Tyr; 
Hb MMilwaukee-1, β67Val→Glu.
6) Hemoglobin C:-( Hb C or HbC) 
abnormal hemoglobin in which substitution of a glutamic acid residue with a lysine residue at the 6th position of the β-globin chain has occurred.
7) Hemoglobin (Hb) Q :-
single nucleotide polymorphism occurring in the Hb α-2 chain.
members of Hb Q family share molecular feature-----the replacement of ASPARTIC ACID (Asp) by HISTIDINE (His) at different positions in the amino acid chain.
These include 
1) Hb Q-Thailand (α74 Asp→His), 
2) Q-India (α64 Asp→His) and
3) Q-Iran (α75 Asp→His).

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