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J. Biol. Chem., Vol. 262, Issue 5, 2138-2145, 02, 1987
OA Bizzozero, JF McGarry and MB Lees
Fatty acyltransferase activity that catalyzes the transfer of palmitic acid
from palmitoyl-CoA to the endogenous myelin proteolipid protein has been
demonstrated in isolated rat brain myelin. Optimum enzyme activity for the
acylation of proteolipid protein was obtained in 0.1% Triton X-100, 2 mM
MgCl2, and 1 mM dithiothreitol at a pH of 7.5 and at 37 degrees C. Other
detergents had little or no effect on the reaction whereas acylation was
completely abolished by sodium dodecyl sulphate (0.1%). Pulse-chase
experiments indicated that the reaction involves the net addition of fatty
acid to the protein and not a rapid fatty acid exchange. The rate of
acylation was linear up to 30 min, indicating that the concentration of
endogenous protein acceptor was constant. Under these conditions and at
short time periods, the enzyme activity versus acyl-CoA concentration
showed a hyperbolic curve. The apparent Km and Vmax for palmitoyl-CoA was
41 microM and 115 pmol/mg protein/min. Similar values were obtained for
stearoyl and oleoyl-CoA, whereas myristoyl-CoA showed a lower specificity
for the enzyme. The acyl-CoA specificity was also studied in competition
experiments using several saturated and unsaturated fatty acid-CoAs. The
product of the reaction was identified as myelin proteolipid protein and
the fatty acid was shown to be attached to the protein via an ester
linkage. Limited proteolysis and peptide mapping showed that the same sites
on the proteolipid protein were acylated when the reaction was carried out
in isolated myelin preparations or in brain tissue slices, suggesting
physiological importance for the in vitro acylation of endogenous myelin
proteolipid protein.
Acylation of endogenous myelin proteolipid protein with different acyl- CoAs
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