title: Phosphorylation and activation of smooth muscle myosin by Acanthamoeba myosin I heavy chain kinase.
abstract: Acanthamoeba myosin I heavy chain kinase activates the actin-activated Mg2+ -ATPase activity of the Acanthamoeba myosin I isoenzymes, myosins IA and IB, by phosphorylating a single site within the myosin heavy chain. In this paper, we report that myosin I heavy chain kinase also phosphorylates isolated turkey gizzard smooth muscle myosin light chains, gizzard smooth muscle heavy meromyosin, and intact gizzard smooth muscle myosin, all in the absence of Ca2+ and with specific activities close to those measured for purified Ca2+/calmodulin-dependent gizzard smooth muscle myosin light chain kinase. Myosin I heavy chain kinase incorporates a maximum of 2 mol of phosphate/mol of heavy meromyosin, both by itself and together with smooth muscle myosin light chain kinase (the light chain kinase alone incorporates 1.6 mol of phosphate/mol of heavy meromyosin). Both kinases phosphorylate intact smooth muscle myosin to a maximum of 2 mol of phosphate/mol of myosin. Myosin I heavy chain kinase fully activates the actin-activated Mg2+ -ATPase of both myosin and heavy meromyosin. Two-dimensional tryptic peptide maps of isolated light chains phosphorylated by myosin I kinase show the same phosphopeptide as for light chains phosphorylated by the light chain kinase. These results support the conclusion that myosin I heavy chain kinase phosphorylates gizzard smooth muscle myosin at the same site within the 20,000-Da light chain as does smooth muscle myosin light chain kinase. The results suggest that the amino acid sequence around the phosphorylation site within the heavy chain of Acanthamoeba myosin I isoenzymes may be similar to the primary sequence around the phosphorylation site within the smooth muscle myosin light chain.
mesh_terms: D000656:Amoeba / Q000201:enzymology*; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004789:Enzyme Activation; D007700:Kinetics; D009130:Muscle, Smooth / Q000201:enzymology; D015879:Myosin Subfragments / Q000302:isolation & purification; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000378:metabolism*; D015800:Protozoan Proteins
chemical_list: D015879:Myosin Subfragments; D015800:Protozoan Proteins; D010770:Phosphotransferases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C033142:myosin-heavy-chain kinase; D009218:Myosins