Abstract
Biochemical properties and some kinetic characteristics of whole-erythrocyte ecto-ATPase (EC 3.6.1.5) were studied in the Black Sea thornback ray Raja clavata L. It was shown that enzyme activity varied from 1.5 to 3.5 nmol Pi/min/μL of packed cells and peaked in the presence of 3.0-6.0 mM Mg2+. Ecto-ATPase exhibited broad substrate specificity towards splitting nucleoside triphosphates. The enzyme was tolerant to changes in ambient pH and exhibited maximum activity in the pH range from 5.5 to 7.7. The enzyme also showed high substrate affinity, with the Michaelis constant (KM) found to be 12.0 ± 1.0 μM and Vmax being 2.35 0.2 nmol Pi/ min/μL of packed cells. Erythrocyte ecto-ATPase in R. clavata was sustainable to erythrocyte storage at 4°C for four days and exhibited a tolerance to high concentrations of urea.
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