Figure 4

Apyrase activity of salivary homogenates of the flea, Xenopsylla cheopis. Reaction media contained 50 mM TrisCl pH 7.4, 150 mM NaCl, 2 mM indicated nucleotide in 100 μl. The reaction started with addition of salivary gland homogenate to give 2.5 pairs per ml. (A) 1 mM CaCl₂ plus 1 mM MgCl₂ were added to the media before starting the reaction. (B) Either 2 mM CaCl₂, 2 mM MgCl₂ or 2 mM EDTA were added to the media before starting the reaction. The bars represent the average ± SE of 3 determinations. All incubations were done at 37°C.