Phosphorylation of smooth muscle heavy meromyosin by calcium-activated, phospholipid-dependent protein kinase. The effect on actin-activated MgATPase activity.
Smooth muscle heavy meromyosin (HMM) can serve as a substrate for the Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) as well as for the Ca2+/calmodulin-dependent kinase, myosin light chain kinase. When turkey gizzard HMM is incubated with protein kinase C, 1.7-2.2 mol of phosphate are incorporated per mol of HMM, all of it into the 20,000-Da light chain of HMM. Two-dimensional peptide mapping following tryptic hydrolysis revealed that protein kinase C phosphorylated a different site on the 20,000-Da HMM light chain than did myosin light chain kinase. Moreover, sequential phosphorylation of HMM by myosin light chain kinase and protein kinase C resulted in the incorporation of 4 mol of phosphate/mol of HMM, i.e. 2 mol of phosphate into each 20,000-Da light chain. When unphosphorylated HMM was phosphorylated by myosin light chain kinase, its actin-activated MgATPase activity increased from 4 nmol to 156 nmol of phosphate released/mg of HMM/min. Subsequent phosphorylation of this phosphorylated HMM by protein kinase C decreased the actin-activated MgATPase activity of HMM to 75 nmol of phosphate released/mg of HMM/min.
D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D002417:Cattle; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D014357:Trypsin / Q000378:metabolism
D000199:Actins; D015879:Myosin Subfragments; D011494:Protein Kinases; D011493:Protein Kinase C; D009219:Myosin-Light-Chain Kinase; D014357:Trypsin; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase