Figure 2. COS BTPC is highly phosphorylated at Ser⁴²⁵.

Co-immunopurified BTPC from stage VII developing COS endosperm was incubated for 20 min in the presence and absence of λ-phosphatase (λ-P'tase) or PP2A_c. (A) Samples were subjected to SDS/PAGE followed by immunoblotting with anti-BTPC or anti-pSer⁴²⁵ antibody, as well as anti-PTPC or anti-pSer¹¹ antibody [17] in the presence of 10 μg/ml of the corresponding dephosphorylated peptide (dephospho) or phosphopeptide (phospho). (B) Samples were subjected to P_i-affinity PAGE followed by immunoblotting with anti-BTPC or anti-pSer425 antibody in the presence of 10 μg/ml dephosphopeptide.