Identification of an activator protein for myosin light chain kinase as the Ca2+-dependent modulator protein.
Myosin light chain kinase which phosphorylates g2 light chain of skeletal muscle myosin requires an activator for the activity (Yazawa, M., and Yagi, K (1977) J. Biochem. (Tokyo) 82, 287-289). This activator has now been identified as the modulator protein known to be a Ca2+-dependent regulator for phosphodiesterase, adenylate cyclase, and ATPases. The identification is based on the quantitative cross-reactivity of muscle activator protein and brain modulator protein in activating myosin light chain kinase and brain phosphodiesterase and identical properties of both proteins in regard to sensitivities to Ca2+, UV absorption spectra, UV absorption difference spectra with or without Ca2+, and mobilities upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the presence of modulator protein, the activity of myosin light chain kinase was reversibly controlled by the physiological concentration of Ca2+. We suggest that two Ca2+-receptive proteins, i.e. modulator protein and troponin-C, may play roles in the contraction-relaxation cycle of skeletal muscle.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004789:Enzyme Activation; D007700:Kinetics; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits
D009124:Muscle Proteins; D011494:Protein Kinases; D009218:Myosins; D002118:Calcium