RELATIONSHIP OF MEMBRANE PHOSPHOLIPID-COMPOSITION, LACTOSYLCERAMIDE MOLECULAR-SPECIES, AND THE SPECIFICITY OF CMP-N-ACETYLNEURAMINATE, LACTOSYLCERAMIDE ALPHA-2,3-SIALYLTRANSFERASE TO THE MOLECULAR-SPECIES COMPOSITION OF GM3 GANGLIOSIDE
H. Kadowaki et Ma. Grant, RELATIONSHIP OF MEMBRANE PHOSPHOLIPID-COMPOSITION, LACTOSYLCERAMIDE MOLECULAR-SPECIES, AND THE SPECIFICITY OF CMP-N-ACETYLNEURAMINATE, LACTOSYLCERAMIDE ALPHA-2,3-SIALYLTRANSFERASE TO THE MOLECULAR-SPECIES COMPOSITION OF GM3 GANGLIOSIDE, Journal of lipid research, 36(6), 1995, pp. 1274-1282
The ceramide molecular species specificity of rat brain neuron CMP-N-a
cetylneuraminate:lactosylceramide alpha 2,3-sialyltransferase (LacCer
alpha 2,3-ST) was determined using 19 molecular species of lactosylcer
amide incorporated into liposomes prepared with purified rat brain pho
spholipids. The neuron enzyme displayed a distinct molecular species s
pecificity (which was different than the specificity of liver LacCer a
lpha 2,3-ST) based on both the long-chain base and the fatty acid comp
osition of the lactosylceramide. Specifically, compared to the liver e
nzyme, relatively high activities were obtained with d18:1-16:0, d18:1
-22:1, and d18:0-18:0 lactosylceramide molecular species. When the lip
id composition of the neuron microsomal membranes was altered to resem
ble that of rat liver Golgi membrane lipids, the activities towards d1
8:1-16:0, d18:1-22:1, and d18:0-18:0 lactosylceramide molecular specie
s were significantly (P < 0.01) reduced and the molecular species spec
ificity of the neuron enzyme resembled that of liver LacCer alpha 2,3-
ST. In the reciprocal experiment in which the lipid composition of the
rat liver Golgi membranes was altered to resemble neuron microsomal m
embrane lipids, the molecular species specificity of liver LacCer alph
a 2,3-ST was virtually identical to the specificity obtained with the
native neuron enzyme. Analysis of the molecular species composition of
lactosylceramide and GM3 in rat liver Golgi membranes revealed that t
he molecular species composition of rat liver Golgi membrane GM3 was p
recisely what would be expected based on the molecular species specifi
city of LacCer alpha 2,3-ST and the molecular species composition of l
actosylceramide in the Golgi membrane. Based on these results, we conc
lude that the molecular species specificity of LacCer alpha 2,3-ST det
ermined in our in vitro assay accurately reflects the specificity of t
he enzyme in vivo and that the specificity of the enzyme is determined
by the phospholipid molecular species composition of the Golgi membra
ne.