Figure 5. Reactivity of tryptic fragments II, III, IV and V in cerebellum, SI(+) and SI(−) type-I IP₃Rs.

Microsomal membranes from cerebellum (Cb) or COS cells transfected with the SI(+) or SI(−) type-I IP₃R construct were incubated with 0.5 mM MPEG-20 for 5 min and then cleaved with trypsin for 5 min as described in the Experimental section. The presence of each of the indicated tryptic fragments was monitored by immunoblotting with the Abs directed at the epitopes depicted in Figure 3. The expected position of the primary tryptic fragment is indicated by the arrowhead and shifted bands are indicated by open circles.