FIGURE 7.

SMTNL1 regulates SMPP1M activity toward myosin. In A, rSMTNL1 was phosphorylated with purified PKA (n = 3; ±S.E.). In B, phosphorylation of Ser-301 was confirmed by phospho amino acid analysis and cleaved radioactive peptide analysis as described (7). In C, SMPP1M activity was measured against ³²P-labeled SM myosin (▵) and rLC20 (○) with or without phospho-SMTNL (filled) or dephospho-SMTNL1 (open). Purified SM myosin and recombinant SM LC20 were phosphorylated with purified SKM MLCK as described (16) (^*, p < 0.001 n = 3; ±S.E.).