The Ca(2+)-dependent binding of Annexin V to phosphatidylserine on cell surfaces 
is a reliable marker for apoptosis that is widely used in flow cytometry based 
apoptosis assays. In this paper, we report a new class of Annexin V-based probes 
for apoptosis. Luciferase from Renilla reniformis (RLuc) was linked to Annexin V 
and expressed successfully in a soluble form in Escherichia coli BL21 (DE3). The 
new probe, Rluc/Annexin V, was purified and functionally assayed for detection 
of apoptosis in actinomycin D-induced apoptotic Jurkat cells. Moreover, the 
spontaneous apoptosis in neutrophils was shown using the new probe. The results 
indicate that Rluc/Annexin V can bind to the apoptotic cells, and the signal of 
Renilla luciferase can be detected by luminometric measurements. The 
availability of Rluc/Annexin V may be of potential commercial interest for 
improving current apoptosis assays.