Hemoglobin of RBCs

HEMOGLOBIN (Hb) :-

🐣Hb is a protein of RBCs.

🐣MW = 65,450 Da, 

🐣Allosteric, oligomeric conjugated protein with 4 polypeptide chains.

🐣Polypeptide chains joined by = non covalent bonds.

🐣Hb = in all vertebrates & in many invertebrates - annelids, many arthropods & some molluscs & expect in Arctic fish.

🐣Four l polypeptide chains  = 2 alfa & 2 beta chains.

🐣One alfa chain  = 141 amino acid residues & one beta chain = 146 a a residues. 

🐣HbA1 =2a & 2b chains (a2b2 gene) - 98% & 2% HbA2 = alpha2 & sigma2 chains (a2s2).

🐣Adult Hb = a2b2 (HbA1) 

🐣Fetal Hb (HbF)  = alpha 2 - gama 2

🐣Early embryonic Hb = epsilon2 - xi2 globin protein.

🐣Embryonic h fetal forms = have higher affinity for O2. 

🐣Hb transport O2 = at the level of tissues.

🐣Two end product of cellular respiration = H+ ion & CO2 also carried by Hb of RBCs.

🐣Hb also perform an important role as a = Buffer & control pH of the blood. 

🐣Hb buffer = because it has both proton doner & proton accepter.

🐣Hb also transport = NO (nitric oxide) 

🐣NO bind at = ferrus O2 binding sites in Hb. 

🐣Binding site of NO = on beta chains of Hb. 

🐣O2 doesn't dissolve easily in water so 1.5% of inhaled O2 dissolve in blood plasma.

🐣About 98.5% O2 carried on Hb. 

🐣1 Hb binds = 4 O2 molecules or 4O2/Hb, because one Hb has 4 globin chains & one globin chain carries one heme group, so 4 globin 4 heme gorup & = binding capacity of O2 is also 4 

🐣Reaction of Hb & O2 = reversible reaction & OXYGENATION not oxidation. 

🐣O2 binds with Hb in = Fe2+ state. 

🐣Fe3+ state doesn't bind O2.

🐣Hb exist in two states = 1. Tense or taut (T) & 2. Relaxed (R) states. 

1. Tense state = deoxy state of Hb, 

🐣Deoxy state stabilized by = no. of ionic interactions.

🐣When one 02 -Hb = it triggers a change in confrontation to R - state. 

2. Relaxed state = O2 - Hb binding with much higher affinity. or

🐣R - state  mean O2 -Hb bounded state. 

🐣T to R transition occurs more readly in second subunit, once O2 is bound to first  subunit. 

🐣Last (4th) O2 -Hb binding affinity = much higher than first molecule.

OXYGEN - HEMOGLOBIN BINDING CURVE :-

🐣Not O2 -Mb like hyperbolic curve,

🐣O2 -Hb binding curve = sigmodial (S - shaped).

🐣For hemoglobin this shape suggests that binding of oxygen at one site within Hb tetramer increases the likelyhood that O2 binds at remaining occupied sites.

🐣O2 -Hb binding = cooperative binding behavior.

🐣Conversely unloading of one Oxygen at one heme = facilitates the unloading  of Oxygen at the others, one by one. 

🐣Binding reaction at each Hb = not interdependent of one another.

🐣Ist O2 -Hb increase affinity of IInd O2 -Hb affinity & oxygenation of IInd Hb increases affinity of IIIrd O2 -Hb so affinity for 4th  O2 -Hb = many times greater than that for the first. 

🐥Next I'll post FUNCTIONAL DIFFERENCES BETWEEN Mb & Hb. 

Thank you so much students for your interest in science.🤗🙏