hemoglobin and myoglobin

hemoglobin

• found in the blood

• oxygen transporter

• tetramer (4 polypeptide chains)

• α-chain= 141 amino acid long

• β-chain = 146 amino acid long

myoglobin

• found in skeletal and cardiac muscles

• oxygen storer

• single polypeptide chain

• 153 amino acid long

what prothetic group is found in both hemoglobin and myoglobin and what is it made of?

heme group is made up of a porphyrin ring and central Fe2+

co-operativity

binding of oxygen to one subunit of hemoglobin strongly enhances binding to oxygen to other subunits

structure of hemoglobin

two dimeric form (α1-β1 subunit make one pair. α2-β2 subunit make another pair)

T-form

tense state

• only accessible to heme group of alpha-chain

• deoxyhemoglobin

• steric hindrance prevents oxygen from binding to beta-chains

R-form

relaxed state

• oxyhemoglobin

• no steric hindrance (all heme is oxygenated)

metmyoglobin

myoglobin with iron in the Fe3+ state

• distal histidine of myoglobin prevents the release of this superoxide iron

• incapable of binding to oxygen

where does oxygen diffuse from?

oxygen diffuses from alveolar air into the blood because the venous blood has a lower partial pressure

how is CO2 transported?

transported in red blood cells primarily as bicarbonate (HCO3-) and is catalyzed within the rbcs by the enzyme carbonic anhydrase

what is bohr effect?

an increase in CO2 and low blood pH decreases hemoglobin’s affinity for O2. this then forces the hemoglobin to unload its oxygen to active tissue that need it most

4 primary oxygen binding regulators

Co2, hydrogen ion (H+), chloride ion (Cl-), and 2,3-bisphosphoglycerate (2,3-BPG)

fetal hemoglobin

α2 γ2 because γ2 doesn’t bind to 2,3-BPG so there is a higher affinity for oxygen, which is crucial for fetuses

oxygen loading and unloading

left shift: increased affinity to O2

right shift: decreased affinity for O2 (pH decreases: acidosis)

sickle-cell anemia

glutamate (hydrophilic) is substituted with valine (hydrophobic) at 6th position of the beta chain