Ruberdoxin MCQs for CSIR, GATE, IIT-JAM

Ruberdoxin MCQs
CSIR-NET | GATE | IIT-JAM

CSIR NET Chemical Sciences - Dec 2011

Q1. In bacterial rubredoxin, the number of iron atoms, sulfur bridges and cysteine ligands respectively are:

1. 4, 4, 4
2. 2, 2, 4
3. 2, 2, 2
4. 1, 0, 4

Correct Answer: 4. 1, 0, 4

GATE Chemistry - 2019

Q2. Match the metalloproteins with their respective functions:
Metalloproteins: P. Ferritin, Q. Rubredoxin, R. Cobalamin, S. Carbonic anhydrase
Functions: I. Electron transfer, II. Acid-base catalysis, III. Metal storage, IV. Methyl transfer

Correct Answer: P–III (Metal storage), Q–I (Electron transfer), R–IV (Methyl transfer), S–II (Acid-base catalysis)

CSIR NET / GATE (Various Years)

Q3. Which of the following statements about rubredoxin is correct?

1. It contains a [4Fe-4S] cluster
2. It contains inorganic sulfide bridges
3. It has a single iron atom coordinated by four cysteine residues with no inorganic sulfide
4. It is involved in oxygen transport

Correct Answer: 3. It has a single iron atom coordinated by four cysteine residues with no inorganic sulfide

CSIR NET / GATE (Various Years)

Q4. The active site of rubredoxin can be described as:

1. [2Fe-2S]
2. [4Fe-4S]
3. [1Fe-0S] or Fe(S-Cys)₄
4. [3Fe-4S]

Correct Answer: 3. [1Fe-0S] or Fe(S-Cys)₄

CSIR NET / GATE (Various Years)

Q5. The number of equivalents of H₂S gas released from the active site of rubredoxin when treated with mineral acid is:

1. 0
2. 1
3. 2
4. 4

Correct Answer: 1. 0
(Rubredoxin has no labile/inorganic sulfide; only cysteine sulfurs, unlike ferredoxins which release H₂S from inorganic S^2- bridges.)

CSIR NET / GATE (Various Years)

Q6. The primary function of rubredoxin is:

1. Iron storage
2. Oxygen transport
3. One-electron transfer
4. Nitrogen fixation

Correct Answer: 3. One-electron transfer

CSIR NET / GATE (Various Years)

Q7. Which of the following is true for rubredoxin?

• A. It contains a single Fe atom in tetrahedral coordination with four cysteine thiolates.
• B. It releases H₂S upon acid treatment.
• C. The iron cycles between Fe(II) and Fe(III), both high-spin.
• D. It is found mainly in aerobic organisms for oxygen binding.

Options:

1. A and B
2. A and C
3. B and D
4. A, C and D

Correct Answer: 2. A and C

GATE Chemistry (Various Years)

Q8. 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. 0, 2, 4
2. 1, 2, 4
3. 0, 1, 2
4. 4, 2, 0

Correct Answer: 1. 0, 2, 4
(Rubredoxin has no labile/inorganic sulfide (0S*), 2-iron ferredoxin ([2Fe-2S]) has 2 labile S, and 4-iron ferredoxin ([4Fe-4S]) has 4 labile S.)

CSIR NET / GATE (Various Years)

Q9. Which of the following iron-sulfur proteins does NOT contain inorganic sulfide (labile sulfur) in its active site?

1. [2Fe-2S] Ferredoxin
2. [4Fe-4S] Ferredoxin
3. Rubredoxin
4. High-potential iron-sulfur protein (HiPIP)

Correct Answer: 3. Rubredoxin
(Rubredoxin has only cysteine thiolates coordinating the single Fe; no inorganic S²⁻ bridges.)

CSIR NET / GATE (Various Years)

Q10. The coordination geometry around the iron center in rubredoxin is best described as:

1. Octahedral
2. Square planar
3. Tetrahedral (slightly distorted)
4. Trigonal bipyramidal

Correct Answer: 3. Tetrahedral (slightly distorted)

CSIR NET / GATE (Various Years)

Q11. The redox process in rubredoxin involves:

1. Fe(II)/Fe(III) couple, both high-spin
2. Fe(III)/Fe(IV) couple
3. Two-electron transfer
4. Low-spin iron states

Correct Answer: 1. Fe(II)/Fe(III) couple, both high-spin
(Minimizes structural rearrangement during electron transfer.)

CSIR NET / GATE (Various Years)

Q12. Consider the following statements about rubredoxin and ferredoxin:

• A. Rubredoxin contains a [1Fe-0S] cluster while ferredoxin contains [nFe-nS] clusters (n=2 or 4).
• B. Rubredoxin releases H₂S upon acid treatment, unlike ferredoxin.
• C. The reduction potential of rubredoxin is generally higher (less negative) than that of bacterial ferredoxins.
• D. Rubredoxin is primarily involved in multi-electron transfer processes.

Correct statements are:

1. A and B
2. A and C
3. B and D
4. C and D

Correct Answer: 2. A and C

CSIR NET / GATE (Various Years)

Q13. The oxidized form of rubredoxin is reddish in color due to:

1. d-d transitions
2. Charge transfer (S → Fe) bands
3. π-π* transitions in aromatic residues
4. Metal-metal charge transfer

Correct Answer: 2. Charge transfer (S → Fe) bands

CSIR NET / GATE (Various Years)

Q14. Which of the following is NOT a characteristic of rubredoxin?

1. Single iron atom coordinated by four cysteines
2. Presence of cubane-type [4Fe-4S] cluster
3. Found mainly in anaerobic bacteria
4. Functions as a one-electron carrier

Correct Answer: 2. Presence of cubane-type [4Fe-4S] cluster
(That is characteristic of [4Fe-4S] ferredoxins.)