A Study of Some Biochemical Properties of Ecto-ATPase (Nucleotidase) in Erythrocytes of the Black Sea Thornback Ray Raja clavata L

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 P i /min/μL of packed cells and peaked in the presence of 3.0-6.0 mM Mg 2+ . 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 ( K M ) found to be 12.0 ± 1.0 μM and V max being 2.35 0.2 nmol P i / 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.