| Species | Original | Mutated to | Mutation |
| Human | Pro 51 |
|
|
| Rat Equivalent | Pro 50 | ||
| Mouse Equivalent | Pro 56 | Ala | P56A |
Mutation resulted in the ablation of specific binding. No labeling was observed when their localization was studied using an antiserum specific for the N terminus of the 5-HT3A.