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GATE 2023 CY – Question 23

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. · 1 mark · Multiple choice

The tetracoordinated copper center in the oxidized and reduced forms of plastocyanin exhibits longest bond with

  1. cysteine-S and methionine-S, respectively
  2. methionine-S and cysteine-S, respectively
  3. cysteine-S and cysteine-S, respectively
  4. methionine-S and methionine-S, respectively

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Correct answer: (D) methionine-S and methionine-S, respectively

Explanation

Plastocyanin has two strong histidineN donors, a strong cysteine thiolate and an axial methionine thioether. The weak axialCu–S(methionine) interaction is longest in both Cu(II) and Cu(I) forms.

Thus **methionine-S in both, D**; redox changes do not make the cysteine bond the longest.