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Abstract
In this study, we have reported the kinetic and biochemical characterization of ectonucleotide pyrophosphatase/phosphodiesterase (E-NPP) activity in rat cardiac fractions, one soluble and the other enriched in vesicles derived from sarcoplasmic reticulum. Both fractions demonstrated E-NPP activities, which could be observed by extracellular hydrolysis of p-nitrophenyl-5′-thymidine monophosphate (p-Nph-5′-TMP) and other biochemical characteristics. The KM values for the hydrolysis of p-Nph-5′-TMP in soluble and microsomal fractions were 118.53 ± 27.28 and 91.92 ± 12.49 µM, respectively. The Vmax values calculated were 2.56 ± 0.15 and 113.87 ± 21.09 nmol p-nitrophenol/min/mg of protein in soluble and microsomal fractions, respectively. Among the compounds tested to evaluate the possible activity of other enzymes on p-Nph-5′-TMP hydrolysis, only suramin (0.25 mM) produced a significant inhibition of substrate hydrolysis. Thus, our results strongly suggest the presence of E-NPP enzymes in subcellular fractions of rat heart, which could be involved in nucleotide signalling in the cardiac tissue.
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Acknowledgements
This work was supported by grants and fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The authors are very grateful to Dr. JJ Sarkis for his supervision during this work and for dedicating his professional life to study the purinergic system.
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.