Phosphatidylinositol Phosphorylation in Fast Skeletal Muscle Membranes
Phosphatidylinositol 4-phosphate (PIP) associated with the isolated Ca2+ transport ATPase from rabbit skeletal muscle sarcoplasmic reticulum (SR) is formed when the enzyme is incubated at high membrane protein concentration with ATP/Mg2+ (1). This observation indicates that an endogenous phosphatidylinositol kinase (PI kinase) is present in these membranes. The PIP formation rate and the steady state level of PIP is enhanced by Phosphorylase kinase, showing that this protein kinase expresses also lipid kinase activity (2,3). It is still unclear what kind of relation exists between the membrane associated PI kinase and the PI kinase present, as side activity, in Phosphorylase kinase.
KeywordsKinase Activity Sarcoplasmic Reticulum Lipid Kinase Sarcoplasmic Reticulum Membrane Phosphorylase Kinase
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