Multiple choice

Which of the following compounds is/are inhibitor(s) for oxygen binding to haemoglobin?

P. CO Q. CO2 R. NO

  1. Only P

  2. Only R

  3. Both P and Q

  4. Both Q and R

  5. All of these

Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Correct answer. Besides the oxygen ligand, which binds to haemoglobin in a cooperative manner, haemoglobin ligands also include competitive inhibitors such as carbon monoxide (CO) and allosteric ligands such as carbon dioxide (CO2) and nitric oxide (NO). The carbon dioxide is bound to amino groups of the globin proteins as carbaminohaemoglobin, and is thought to account for about 10% of carbon dioxide transport in mammals. Nitric oxide is bound to specific thiol groups in the globin protein to form an S-nitrosothiol, which dissociates into free nitric oxide and thiol again, as the haemoglobin releases oxygen from its heme site. This nitric oxide transport to peripheral tissues is hypothesised to assist oxygen transport in tissues, by releasing vasodilatory nitric oxide to tissues in which oxygen levels are low.

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