An Active Form of Sphingosine Kinase-1 Is Released in the Extracellular Medium as Component of Membrane Vesicles Shed by Two Human Tumor Cell Lines

Table 1

Enzimatic assay of SphK-1 activity.

Sample	Incubation mixture with exogenous sphingosine	Incubation mixture without exogenous sphingosine
SK-Hep1 vesicles	43.93 pmol/min/mg of protein	26.70 pmol/min/mg of protein
SK-Hep1 vesicles∗	43.59 pmol/min/mg of protein
SK-Hep1 C.M.	2.23 pmol/min/mg of protein
8701 BC vesicles	14.44 pmol/min/mg of protein	12.61 pmol/min/mg of protein
8701 BC vesicles∗	16.70 pmol/min/mg of protein
8701 BC CM	2.16 pmol/min/mg of protein

*Vesicles recovered from medium in which 2 M NaCl had been added.