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GATE 2022 CY – Question 43

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 choice

The number of equivalents of H2S gas released from the active site of rubredoxin, 2-iron ferredoxin, and 4-iron ferredoxin when treated with mineral acid, respectively, are

  1. 4, 6, 8
  2. 0, 2, 4
  3. 1, 2, 4
  4. 0, 2, 3

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Correct answer: (B) 0, 2, 4

Explanation

Rubredoxin has only cysteine thiolate ligands, whose protonation does not liberate inorganic H2S. The[2Fe–2S] and[4Fe–4S] clusters contain two and four inorganic sulfides, respectively; acid converts these to H2S.

Thus **0,2,4, B**. Protein-bound organic sulfur is not counted as acid-labile cluster sulfide.