Figure 3. Diagram illustrating the intact and trypsin-fragmented type-I IP₃R.

The upper diagram shows the intact receptor. The approximate locations of the three known splice sites (SI, SII, SIII), the ligand binding domain (LBD) and the six transmembrane helices are indicated (vertical bars). The lower diagram shows the approximate molecular-masses of the five tryptic fragments. Their amino-acid boundaries are indicated at the beginning of each fragment. Both fragment I and fragment IV have two alternative molecular-masses depending on the presence or absence of the spliced sequences present within these fragments. Also shown are the epitopes and names of the Abs used to detect the individual fragments.