Identification of a nucleotide pyrophosphohydrolase from articular tissues in human serum

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Abstract
Objective. To characterize the nucleotide pyro‐phosphohydrolase (NTPPHase) in human serum. Methods. NTPPHase activity and kinetic analysis were performed using thymidine monophosphate paranitrophenyl ester (TMPNP) or 32Pγ‐labeled ATP as substrate. Sera were chromatographed (dye column), and peak fractions were analyzed kinetically and by immunoblot using antibodies to 127‐kd articular cartilage vesicle (ACV) NTPPHase as well as to PC‐1 and to 58 kd, two plasma membrane ecto‐NTPPHases. Enzyme activity was measured before and after sample ultracentrifugation. Results. NTPPHase activity was found in all sera tested (2 normal subjects, 9 arthritis patients). Specific activity was increased 9–32‐fold after chromatography; 60–80% of total activity was recovered in a single peak containing an ∼100‐kd soluble peptide related to the 127‐kd ACV enzyme. The apparent Km of this peptide (TMPNP) was virtually identical to that of the porcine ACV 127‐kd enzyme. No immunoreactivity against PC‐1 or 58‐kd NTPPHase was found. Conclusion. Human serum NTPPHase is derived from 127‐kd ACV‐related enzyme.