Figure 2

C-terminal deletion mutants showed high photoactivity. HEK cells expressing WT, Oa-360, and Oa-348 were exposed to blue light, and the resulting cAMP-dependent luminescence was detected. (a) Representative sequential luminescence images after illumination. The inset shows quantitative plots of luminescence intensities after exposure to blue light at 4.5 × 10² µmol m⁻² s⁻¹ for 20 s. Under the same irradiation condition (4.5 × 10² µmol m⁻² s⁻¹ for 20 s), the luminescence of Oa-348 and Oa-360 was obviously high, while that of the WT was mostly undetectable. The luminescence of the WT was clearly detected by longer exposure to more intense blue light (5.7 × 10³ µmol m⁻² s⁻¹, 60 s). (b) Time course of cAMP-dependent luminescence intensities (left) and integrated luminescence intensities (right) at indicated blue light intensities. C-terminal deletion mutants were activated by weaker blue light intensities, and they produced a larger amount of cAMP than the WT.