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A new fluorimetric enzyme assay for the diagnosis of Niemann–Pick A/B, with specificity of natural sphingomyelinase substrate
Author(s) -
Diggelen O. P.,
Voznyi Ya. V.,
Keulemans J. L. M.,
Schoonderwoerd K.,
Ledvinova J.,
Mengel E.,
Zschiesche M.,
Santer R.,
Harzer K.
Publication year - 2005
Publication title -
journal of inherited metabolic disease
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.462
H-Index - 102
eISSN - 1573-2665
pISSN - 0141-8955
DOI - 10.1007/s10545-005-0105-y
Subject(s) - acid sphingomyelinase , substrate (aquarium) , niemann–pick disease , sphingomyelin , enzyme , substrate specificity , biochemistry , sphingomyelin phosphodiesterase , microbiology and biotechnology , chemistry , biology , membrane , ecology , cholesterol
Summary 6‐Hexadecanoylamino‐4‐methylumbelliferylphosphorylcholine (HMUPC) was shown to be a specific substrate for the determination of acid (lysosomal) sphingomyelinase (ASM; gene SMPD1 ). Fibroblasts ( n = 27) and leukocytes ( n = 8) from both the A and B types of Niemann–Pick disease showed < 6% and < 10% of mean normal ASM activity, respectively. Niemann–Pick A or B” appears to be used with a very specific meaning. The Summary should be able to stand entirely alone from the text: should the use of this notation be expanded/explained more fully here in the Summary [or is the phrase “bearing the Q292K mutation” sufficient]?} patients bearing the Q292K mutation had apparently normal ASM activity with our new artificial substrate. These patients with false‐normal sphingomyelinase activity, however, could readily be detected by determining the extent of inhibition of enzymatic hydrolysis of the artificial substrate HMU‐PC by an unlabelled natural substrate, in particular lysosphingomyelin. This approach is generally applicable. Our novel assay for ASM combines the ease of a rapid and robust enzyme assay using a fluorogenic substrate with the specificity of an ASM assay using a natural substrate. Such assays are obviously more convenient to the diagnostic laboratory, since radiolabelled substrates are not required.