Tandem Mass Spectrometry Assays of Palmitoyl Protein
Thioesterase 1 and Tripeptidyl Peptidase Activity in Dried Blood Spots
for the Detection of Neuronal Ceroid Lipofuscinoses in Newborns
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Abstract
We report new substrates for quantitative
enzyme activity measurements
of human palmitoyl protein thioesterase (PPT1) and tripeptidyl peptidase
(TPP1) in dried blood spots from newborns using tandem mass spectrometry.
Deficiencies in these enzyme activities due to inborn errors of metabolism
cause neuronal ceroid lipofuscinoses. The assays use synthetic compounds
that were designed to mimic the natural substrates. Incubation produces
nanomole quantities of enzymatic products per a blood spot that are
quantified by tandem mass spectrometry using synthetic internal standards
and selected reaction monitoring. The assays utilize a minimum steps
for sample workup and can be run in a duplex format for the detection
of neuronal ceroid lipofuscinoses or potentially multiplexed with
other mass spectrometry-based assays for newborn screening of lysosomal
storage disorders