MECHANISM OF G(M3) GANGLIOSIDE SYNTHESIS - KINETIC-STUDY OF RAT-LIVERCMP-N-NEURAMINATE-LACTOSYLCERAMIDE ALPHA-2,3-SIALYLTRANSFERASE EMPLOYING 19 MOLECULAR-SPECIES OF LACTOSYLCERAMIDE
H. Kadowaki et Ma. Grant, MECHANISM OF G(M3) GANGLIOSIDE SYNTHESIS - KINETIC-STUDY OF RAT-LIVERCMP-N-NEURAMINATE-LACTOSYLCERAMIDE ALPHA-2,3-SIALYLTRANSFERASE EMPLOYING 19 MOLECULAR-SPECIES OF LACTOSYLCERAMIDE, The Journal of biological chemistry, 269(21), 1994, pp. 14931-14938
The apparent K-m and V-max of CMP-N-acetylneuraminate:lactosylceramide
alpha 2,3-sialyltransferase (LacCer alpha 2,3-ST) for lactosylceramid
e and CMP-N-acetylneuraminic acid were determined using 19 molecular s
pecies of lactosylceramide. The K-m for lactosylceramide varied 6-fold
among these molecular species of lactosylceramide, but there was a po
or correlation between the K-m for a particular molecular species and
the activity of LacCer alpha 2,3-ST for that molecular species. The K-
m for CMP-N-acetylneuraminic acid also varied depending on the molecul
ar species of lactosylceramide used as substrate, and there was a good
correlation between the K-m of LacCer alpha 2,3-ST for CMP-N-acetylne
uraminic acid and the activity of the enzyme. Kinetic studies indicate
that the reaction mechanism of LacCer alpha 2,3-ST is a sequential, O
rdered Bi Bi system. From considerations of the effects of the structu
re of the lactosylceramide molecular species on the V-max and K-m for
CMP-N-acetylneuraminic acid, it is likely that LacCer alpha 2,3-ST fir
st binds lactosylceramide and then CMP-N-acetylneuraminic acid and tha
t the rate-limiting step in the reaction is the release of the product
G(M3).