In haemoglobin, the transition from T state to R state is triggered by:
oxygen binding.
heme binding.
Proton Binding
Carbamate modification
subunit dissociation.
The correct answer and explanation is:
The correct answer is oxygen binding.
Hemoglobin undergoes a transition between two states: the T (tense) state and the R (relaxed) state. This transition is crucial for its function in transporting oxygen. The T state represents the deoxygenated form of hemoglobin, and it has a lower affinity for oxygen. In contrast, the R state is the oxygenated form, with a higher affinity for oxygen. The transition from the T state to the R state is triggered by oxygen binding.
Here’s how it works:
Hemoglobin is a tetramer composed of four subunits, each containing a heme group that can bind oxygen. When one oxygen molecule binds to a heme group in the T state, it causes a conformational change in that subunit. This change is transmitted to the other subunits, which results in the overall transition of the hemoglobin molecule from the T state to the R state. The R state has a higher affinity for oxygen, which facilitates the binding of additional oxygen molecules. This is known as cooperative binding.
The mechanism behind this transition is related to the structural changes in the heme group upon oxygen binding. In the T state, the heme is somewhat puckered, but when oxygen binds, it pulls the iron ion in the heme closer to the center of the porphyrin ring, leading to a flattening of the heme. This change in shape alters the positioning of the protein subunits, making the R state more favorable for oxygen binding.
Other factors, like proton binding, carbamate modification, and heme binding, play roles in regulating hemoglobin’s affinity for oxygen under different conditions, such as in tissues with high CO2 concentrations or low pH. However, the primary trigger for the T-to-R transition is oxygen binding.