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Characterization and Developmental Expression of Lactotriosylceramider: Galactosyltransferase for the Synthesis of Neolactotetraosylceramide in the Nervous System
Author(s) -
Chou Denise K. H.,
Jungalwala Firoze B.
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.62010307.x
Subject(s) - cerebral cortex , cerebellum , galactosyltransferase , white matter , enzyme , biochemistry , cerebellar cortex , glycolipid , cortex (anatomy) , biology , specific activity , cerebrum , enzyme assay , galactose , central nervous system , medicine , chemistry , endocrinology , neuroscience , radiology , magnetic resonance imaging
Neolactoglycolipids are derived from neolactotetraosylceramide (nLcOse 4 Cer). They are found during the embryonic and neonatal developmental periods in the rat cerebral cortex and disappear shortly after birth. These glycolipids are, however, abundant in the adult cerebellum. Lactotriosylceramide (LcOse 3 Cer):galactosyltrans‐ ferase (GT), which catalyzes the terminal step in the biosynthesis of nLcOse 4 Cer, was characterized in mammalian brain. The enzyme was highly specific for LcOse 3 Cer, with a terminal GlcNAcβ1 ‐3Gal‐residue, and it did not catalyze the transfer of galactose to other glycolipids studied with alternate carbohydrate residues. The microsomal membrane enzyme required Mn 2+ and a detergent for in vitro activity. The optimal pH was 7.4, and the K m value for LcOse 3 Cer was 34 μ M (V max =∼2 nmol/mg/h). The LcOse 3 Cer:GT was shown to be different from the GM2:GT and the soluble enzyme lactose synthase A. The specific activity of LcOse 3 Cer:GT was enriched fivefold higher in the white matter than in the gray matter of young adult rat brain, whereas GM2:GT was enriched only about 1.5‐fold higher in the white matter. The developmental expression of LcOse 3 Cer:GT in the cerebral cortex and cerebellum was not correlative with the levels of nLcOse 4 Cer in these neural areas. Despite the complete absence of nLcOse 4 Cer in the cerebral cortex of animals older than 5 days, significant activity of the LcOse 3 Cer:GT was found even in the adult cortex. In cerebellum, the levels of nLcOse 4 Cer increased with development, but the specific activity of the enzyme was reduced by 50% soon after birth and then remained practically the same with development. The results indicate that LcOse 3 Cer:GT is not a regulatory enzyme that controls the expression of nLcOse 4 Cer and its derived neolactoglycolipids in the brain.