C-Phycocyanin (C-PC)¹ occurs as the major phycobiliprotein in many cyanobacteria and as a secondary phycobiliprotein in some red algae. The pigment has a single visible absorption maximum at 620 nm and a fluorescence emission maximum at ~642 nm. It shows two bands corresponding to α (21,360 Da) and β (18,980 Da) subunits on SDS-PAGE². These two subunits usually occur in equal numbers, but the exact number of α and β pairs may vary among the species.In addition to absorbing light directly, this intensely blue pigment accepts quanta from phycoerythrin (Cat# AS-82001 and Cat# AS-82004) by fluorescent energy transfer in organisms in which PE is present. The red fluorescence of C-PC can be further transferred to allophycocyanin (Cat# AS-82000).The molar extinction coefficient of C-PC at 620 nm is 1.54 x 10⁶ cm^-1M^-1. C-PC is supplied in sodium phosphate buffer, pH 7.0, with ammonium sulfate. The protein is very stable and can be stored for years in this buffer.Before use, centrifuge the C-PC suspension at 10, 000 g for 10 min at 4 ℃. Discard the supernatant and resuspend the pellet into the desired buffer. Store C-PC and C-PC related conjugates at 4 ℃ and keep away from light.