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RAT BRAIN β‐GALACTOSIDASES: OBSERVATIONS ON CEREBROSIDE‐β‐GALACTOSIDASE CATALYSED TRANSGALACTOSYLATION AND COMPARISON OF ASSAY METHODS FOR SPHINGOLIPID HYDROLYSIS
Author(s) -
Carter T. P.,
Kanfer J. N.
Publication year - 1976
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 - 10.1111/j.1471-4159.1976.tb01543.x
Subject(s) - cerebroside , ceramide , sphingosine , galactoside , chemistry , biochemistry , sphingolipid , hydrolysis , galactosyltransferase , galactosidases , enzyme , galactose , beta galactosidase , gene expression , apoptosis , receptor , gene
— A partially purified rat brain preparation, enriched in cerebroside β‐galactosidase activity, was found to catalyze the synthesis of labelled galactosyl‐ceramide from [ 14 C]oleoyl‐sphingosine as acceptor and several β ‐galactosides as donor. The following compounds in the order of their effectiveness served as galactose donors for this reaction: para‐nitrophenyl‐β ‐galactoside (PNP‐β ‐gal), galactosyl‐ceramide, lactosyl‐sphingosine, lactosyl‐ceramide, 4‐methyl‐umbelliferyl‐β ‐galactoside (4‐MU‐β ‐gal). asialo‐G M1 , galactosyl‐sphingosine, G M1 and monogalactosyl‐diglyceride. It is believed that this transgalactosylation reaction is probably not a mere reversal of the hydrolytic reaction. Under optimal conditions the quantity of galactosyl‐ceramide formed represented 10% of the amount of donor hydrolysed. These observations in conjunction with those on the hydrolyses provide further support for the possible existence of two β ‐galactosidase isoenzymes involved with the catabolism of G M1 and/or lactosyl‐ceramide, and a single form for galactosyl‐ceramide. The activity of one isoenzyme can be ‘selectively’ measured simply by modifying the incubation mixture.