Subject(s)
Brain Stem/enzymology , Calcium/pharmacology , Magnesium/pharmacology , Myelin Basic Protein/metabolism , Myelin Sheath/enzymology , Protein Kinases/metabolism , Animals , Egtazic Acid/pharmacology , Kinetics , Male , Octoxynol , Phosphorylation , Polyethylene Glycols/pharmacology , Protease Inhibitors/pharmacology , Rats , Sodium Fluoride/pharmacologyABSTRACT
Polypeptide composition and endogenous phosphorylation were investigated in the subfractions of rat brain myelin isolated by either discontinuous or continuous sucrose density gradient centrifugation of myelin. Similarly, a myelin-like membrane fraction (SN4) was also studied. Observations were made that strongly indicated the presence of a calcium-stimulated protein kinase in a highly purified myelin preparation and which exclusively phosphorylated myelin basic proteins of the membrane preparation. Adenosine cyclic 3',5'-phosphate (cAMP) stimulated kinase on the other hand was found to be considerably enriched in the myelin-like membrane fraction. Although this latter enzyme is also capable of phosphorylating the basic proteins, its effect was at least 5 times weaker compared to the calcium-stimulated myelin protein kinase. Within the gradient subfractions there appeared a close relation between the amount of basic proteins and their calcium-stimulated phosphorylation; a similar relationship, however, was not obtained in the case of cAMP-dependent phosphorylation of myelin basic proteins. The former (i.e., Ca2+-stimulated phosphorylation) was found to require a protein factor that functionally resembled calmodulin. The results thus raises an interesting possibility of the presence of calmodulin-like proteins and a calcium-stimulated protein kinase in adult myelin membrane from mammalian brain, both of which have been hitherto unrecognized constituents of myelin membranes.
Subject(s)
Brain/enzymology , Myelin Basic Protein/metabolism , Myelin Sheath/enzymology , Protein Kinases/metabolism , Animals , Calcium/physiology , Calmodulin , Centrifugation, Density Gradient , Electrophoresis, Polyacrylamide Gel , In Vitro Techniques , Male , Phosphorylation , RatsABSTRACT
Myelin isolated from the central and peripheral nervous system contains a Mg2+-dependent protein kinase that catalyses phosphorylation of myelin-specific proteins. This phosphorylation is markedly stimulated by Ca2+ but not by cyclic AMP. Evidence was obtained that suggested an involvement of calmodulin-like protein in the stimulatory effects of Ca2+ on myelin phosphorylation.
