Hemoglobin exists in two principal conformational states: the T-state (tense) and the R-state (relaxed). Which statement about these states is correct?
- A The T-state has higher oxygen affinity and fewer salt bridges between subunits
- B The R-state is the deoxygenated conformation stabilized by 2,3-BPG
- C The T-state is the low-affinity deoxygenated conformation with more intersubunit salt bridges ✓
- D The T-state and R-state have identical oxygen affinities but differ in heme iron position
Correct answer: C. The T-state is the low-affinity deoxygenated conformation with more intersubunit salt bridges
Explanation
The T-state is the low-affinity deoxygenated conformation stabilized by salt bridges between subunits (including those involving beta-146 His and alpha-40 Lys). The R-state is the high-affinity oxygenated conformation with broken salt bridges. 2,3-BPG stabilizes the T-state, not the R-state. The two states differ markedly in oxygen affinity.
Reference: Harper's Biochemistry, 31st ed.
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