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GATE 2023 CY – Question 52

Inorganic Chemistry · Bioinorganic Chemistry: Ion (Na+ and K+) transport, oxygen binding, transport and utilization, electron transfer reactions, nitrogen fixation, metalloenzymes containing magnesium, molybdenum, iron, cobalt, copper and zinc. · 2 marks · Multiple select

The correct statement(s) regarding myoglobin (Mb) and haemoglobin (Hb) is(are)

  1. At low partial pressure of O2 (e.g., 5 kPa), the O2 affinity of Hb lowers upon lowering the pH
  2. Binding of the first O2 molecule to Hb results in lower affinity for the binding of second O2 molecule
  3. Metal center in deoxy-Mb is low-spin whereas it is high-spin in the case of oxy-Mb
  4. One end of O2 binds to the metal center in oxy-Mb and the other end of the bound O2 is H-bonded with imidazole-NH of a distal histidine

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Show answer and explanation

Correct answer: (A) At low partial pressure of O2 (e.g., 5 kPa), the O2 affinity of Hb lowers upon lowering the pH; (D) One end of O2 binds to the metal center in oxy-Mb and the other end of the bound O2 is H-bonded with imidazole-NH of a distal histidine

Explanation

Lower pH reduces Hb oxygen affinity through the Bohr effect, A true. Hb binding is positively cooperative, so first O2 increases subsequent affinity, B false. DeoxyMb is high-spin and oxyMb is low-spin, opposite C. The distal histidine hydrogen-bonds to the terminal bound oxygen atom, D true. **Select A, D**.