Different properties of two types of red fluorescent proteins in octocoral, Scleronephthya spp. as Akane families.

We report the different properties of two types of red fluorescent proteins (RFP), undescribed species, extracted from two octocorals, Scleronephthya sp. 1 (S. sp. 1) and S. sp, 2 (Alcyonacea, Nephtheidae). S. sp. 1, named Alc-Orange, emits strong green emission at 492 nm and weak red emission at 590 and 630 nm when excited at 449 and 574 nm, respectively. S. sp. 2, LS-Red, emits strong deep red at 642 nm and weak green at 480 and 510 nm when excited at 574 nm and 434 nm, respectively. LS-Red has a very large Stokes shift of about 208 nm emitting at 642 nm when excited at 434 nm. Interestingly, LS-Red shows some emissions at 480 (blue emission), 514 (green emission), 563 (orange emission), and 642 nm (deep red emission) continuously at pH 7.5, which means multicolored fluorescence protein by one excitation at 434 nm. In pH dependence of fluorescence of Alc-Orange (pH 13 to 3.5), no relation between 'green and red FPs' was observed, whereas LS-Red showed the interconversion between 'green and red forms' depending on pH (11.5 to 4.5).