Journal of Lipid Research, Vol 30, 1789-1797, Copyright © 1989 by Lipid Research, Inc.
Lactosylceramide molecular species specificity of rat liver CMP-N- acetylneuraminate:lactosylceramide sialyltransferase
H Kadowaki, LA Symanski, KE Rys-Sikora and RS Koff
Department of Medicine, Framingham Union Hospital, MA 01701.
Six naturally occurring and three synthetic molecular species of
lactosylceramide (LacCer) were used to examine the molecular species
specificity of CMP-N-acetylneuraminate:lactosylceramide alpha 2,3-
sialyltransferase in a Golgi-rich fraction of rat liver. The enzyme
molecular species specificity was determined either in the presence of
nonspecific lipid transfer protein or in the presence of detergents. Assays
performed in the presence of transfer protein showed that for those
lactosylceramide molecular species with either d18:1 or d18:0 long chain
base the enzyme activity decreased linearly as the effective carbon number
of the fatty acid increased. An increase in the carbon number of the long
chain base decreased the activity of the enzyme twice as much as a
corresponding increase in the carbon number of the fatty acid. On the other
hand, when the enzyme activity was assayed in the presence of detergents,
there was no significant difference in activity among the various molecular
species of lactosylceramide based upon the carbon number of the fatty acid
or on the presence of a double bond in the long chain base. However, the
decrease in enzyme activity with an increase in the carbon number of the
long chain base persisted. These results demonstrate that sialyltransferase
has binding specificity with respect to the long chain base, but not the
fatty acid. The apparent molecular species towards the fatty acid is
related to the aqueous solubility of the various LacCer molecular species.
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